I am not an expert on this topic, so I will only tell you exactly what I know from having been one of the first few hundred people to buy the porcelain and vinyl Franklin Mint Princess Diana dolls and outfits when The Mint first offered them to the general public. 

  The outfits were, at first, 16" doll-sized reproductions ( for the vinyl dolls; the others for the 18"to 21" porcelains) of the dresses bought by The Franklin Mint and other doll companies at the Christies' Dress Auction in June of 1997. The first few hundred buyers of the "Travolta" dress received a necklace and earrings with real tiny (but real) sapphires as a special "thank you" from The Mint. As an early buyer of "The Princes of Glamour" doll, for example, as well as the Travolta (and other dolls and outfits) the faux pearl necklace I got had a real sapphire in the middle, surrounded by a tiny circle of real diamonds, then later white sapphires before they were made with cubic zirconia.  The later necklaces have larger faux "sapphire" middle stones and faux "diamonds"

   As The Mint began to sell more of these two outfits and dolls, the jewels in the earrings and necklaces was no longer sapphire or diamond, but fine Austrain crystal...still not bad! The Travolta doll came with a vague "replica" (or interpretation) of a necklace and earring set given to Diana by the Sultan of Brunei. In the pictures of Diana wearing this set, including a matching bracelet, it looked to be a sleek omega-type diamond-encrusted necklace with a gorgeous "wave" of sapphires in its middle section. The FM version, especially the one with real sapphires and Austrian crystals, is very nice, but it was not the famous pearl and sapphire choker we expected to see with the "Travolta" dress. The bracelet is lovely, but does not match the necklace and earrings. The earrings look the most like the Real Thing.

   The Princess of Glamour wears the famous faux pearl and (for we lucky few first buyers) real sapphire choker, again surrounded by teeny-tiny diamonds. Then, faux pearls and crystal "sapphire and diamonds" were used in the rest of this vinyl doll's jewelry.

   The porcelain "Elvis" dress doll wears the pearl choker with the large center sapphire surrounded by crystals, along with one of the largest of the replica Queen Mary tiaras. (They have gotten smaller on other Diana dolls oferred later, such as the Diana sitting on a cushion.) The Spencer tiaras have remained roughly the same size, but do vary with the particular outfit and doll company  involved. The Franklin Mint really has the best replicas of these two famous tiaras which Diana wore.

  The way to tell if you own a necklace with real sapphires is fairly simple: Just look at the silver back of the circle. If the letters "FM" and the numbers "925" are there, you've got a sterling silver necklace with real sapphires. If the backing says "FM" and "China" on it, then the stones are not real gems, but beautiful crystals, which are nice, but...Hey! They're still unique to The Princess!

    The original documentation, if you have it, will tell you what you have. If you buy second-hand, the documentation may be original, but the doll may not. Look ON THE DOLL's side for a true Limited Edition number. If it IS a true Limited Edition, it will have the name of the doll as well as a number, printed on the doll's side: Eg: Diana, Princess of Grandeur, "335/5,000" What that number means is that you have the 335th doll produced by The Mint out of the total of 5,000 made in that edition.

    Others, who are more expert than I, can tell you how many dolls were made in the editions done by several mints and doll companies. I think The Franklin Mint did the overall best job of depicting the Dresses and jewels worn by Princess Diana. But The Danbury Mint's original Diana doll has her wearing the dress she wore when on tour with Prince Charles in Austrailia when he zoomed her across the dancefloor and she wore her emerald and diamond tiara as a headband. The Danbury Mint also lovingly reproduced the Royal Ribbon worn depicting a lovely and detailed tiny image of Queen Elizabeth II on it. That ribbon and image of The Queen are very true to life.

   Many people are switching Jackie Kennedy and Diana clothes, and even Gene doll clothes. Look for an auction where Ltd. Editions are stated and where the dresses are attributed to the right original dolls.  If the people are not sure, then the doll has probably passed through many owners. This is not a bad thing if the doll and its papers are real and everything is in order, or if you just like the doll. BUT, if you ask the Seller, he or she should tell you if the doll was originally acquired by them and/or if everything that is supposed to be there is there. If they say that they honestly don't know, then look for the hallmarks mentioned above when you get the doll. If the Seller has no idea, then you can ask them to look on the back of the necklaces, or on the sides of the dolls and they should tell you. ALSO Sellers have to tell potential buyers if there are any marks or stains on the doll's body. These marks often are the result of long-term storage of the doll, especially if the doll is wearing dark clothing. But other colors do stain vinyl dolls, so ask about this, just to make sure. The Porcelain dolls don't stain nearly as easily, if at all.

    One thing to watch for are COAs. Match them to the dolls. Some people are selling just the COAs, which others are including with their dolls. This is confusing at best, and misleading at worst. It IS nice to have a COA with your doll or dress ensemble. Just check the number (if the doll is a limited edition) printed on the doll's side to see if it is,indeed, a low number. That would best indicate if your doll is, indeed, an early edition, or a Limited Edition

   Not being an expert, I've probably left-out some salient points. But at least you'll be able to ID some of the jewels, outfits and Limited Editions, as those were some of the major selling points made by the Franklin Mint in their early Diana/Jackie doll-selling days.

    There is one more thing I do know about the Franklin Mint porcelain dolls. The legs MUST be packed VERY securely or they WILL BREAK. I know that to my cost (three Princesses of Style arrived with broken legs, which was very depressing). The earrings on some of the porcelain dolls (along with the glued-on wigs) can be removed should you get a broken doll and wish to re-dress another Diana doll, using these materials. But some earrings are firmly glued onto the porcelain dolls, so ask your seller to please pack these precious beauties as carefully as possible!

    If you get a porcelain doll with a long-sleeved outfit, check to see if the arms are made of cloth or porcelain under the sleeves. If the arms are made of cloth, they can be safely bent to new and more realistic positions. And some of the outfits can be changed, but at your own risk, as porelain hands, arms, etc can break. There is one porcelain doll with a lovely face, but whose dress, although part of the Christies' Dress Auction, is not popular. In person it is a gorgeous crepe dress, but it doesn't translate well in the pictures I've seen of it. The face of that doll is very, very beautiful. It has a gentle serenity that many of the other, more "generic" Diana faces lack.

   Another thing I should mention is that, at first, the dresses that came from those the various doll companies were bought at the Christies' Auction. Then, The Princess Diana Trust, headed by the now reviled "porous rock" Paul Burrell, WASTED MILLIONS of pounds from this fund by suing the doll companies for reproducing the dresses. So millions of the monies donated to The Trust by the Mint, as well as by people the world over who wanted to add even more meaning to Diana's life by giving whatever they could, which were supposed to directly support The Princess' charities, evaporated into thin air. The Trust Fund is now administered by Diana's sister, Lady Sarah, whom Diana always adored. Mr. Burrell, revealed by his own testimony and that of others to have allegedly STOLEN a ring from Princess Diana's lifeless finger whilst "gurading" her remains before her funeral, is now living in Florida. I ask you as a personal favor NOT to support Burrell in any way, as his "information" about The Princesss is totally tainted BY HIS OWN ADMISSION.

    The Trust LOST their lawsuit, because the doll companies rightly owned those dresses and they could do with them what they would, including reproducing them. So now, the dresses you see from The Mint are not only reproductions of the ones they bought at The 1997 auction, but also include others which differ from those at the Auction. The documentation should tell you which dresses are authentic reproductions of Diana's "real" dresses. Some of the dresses now being sold are very nice and excellent reproductions of later dresses that The Princess actually wore, but which were not included in the 1997 Auction. 

    And some of them are fabrications of the dollmakers' imaginations. IF they look enough like the dresses which Diana actually wore, and the Seller is "up front" about this, and YOU ADORE "the look" because it captures even a whiff of that charisma which was Princess Diana's heart and soul, and which STILL LIVES ON in so many of our hearts the World over, then there should be no problem...as long as you know and are comfortable with what you are buying.

    An honest seller will tell you from where the dress came. The Danbury and Franklin Mint's reproductions are fairly true to to the originals, as were the Gadco dolls. So look for old magazine (and newer books) for actual pictures of The Princess wearing a particular dress if you see a dress that doesn't look like Diana's. The Seller should state what collection the doll's dress comes from, and should be able to answer that question for you. If the Seller doesn't know, then he or she or they, will tell you that too. Sometimes a seller will tell you something which you later find is not strictly true, but which the seller believes to be true. Thus, both  Buyers and Sellers need to do their homework... The dolls and outfits are all gorgeous, but it is nice to know what you are bidding for, if at all possible.

   The Franklin Mint contributed $4 million to the very fund which foolishly squandered millions of pounds on fruitless lawsuits. NOW the Franklin Mint may or may not be contributing a percentage of their sales back to the Fund, but I find it a sad thing to know that the money which The Mint and thousands of us contributing to this fund when buying our original dolls was wasted in a way which would have really shocked and saddened The Princess.

   The original dresses which were bought by private collectors were sold and resold in many cases. Many of them are now part of one (and now perhaps a few more of the 1997) buyer's Dresses For Humanity program where the dresses are still viewed in cities across the globe in an ongoing and  hugely successful effort to raise millions to be directly donated to The Fund which supports the charities and causes which were so dear to The Princess' heart.

    I have "followed" the comings and goings of Great Britain's Royal Family for most of my life. I've also had several letters published in Majesty Magazine, the latest one in the August, 2008 issue. This magazine closely reports issues relating to Royals the world over, but focuses most prominently on Great Britain's Royal Family. I have also read many, many books and newspaper and magazine articles about Princess Diana, as well as Prince Charles, Camilla, The Royal Family, Princess Margaret, the Royal Residences, and, of course, Queen Elizabeth II (as well as the Duke and The Duchess of Windsor), etc.. The Family geneology links everyone in it, and it is not often mentioned that Princess Diana and The Queen Mother AND Prince Charles himself share a few common ancestors. BOTH The Queen and her husband can claim Queen Victoria as a common great-great (etc.) Grandmother! In contrast, Princess Diana's bloodline brings a fresh, and much deeper Royal lineage as her gift to her sons and The United Kingdom.

    Princess Diana's heritage goes even further back than that of Prince Charles, a fact which was reported to have annoyed him very much!

    So, I believe I have some real sense of the historical importance of just how deeply Princess Diana cut her own swath across the future of The Monarchy.And in many cases, she used her fashion sense to do this. Her dresses are more than "dresses:" Each one is a Statement, fit for each occasion for which she wore them. She chose her fashions to carefully craft the Image she wished to portray, and the clothes which she wore to other countries almost always carried a theme, denoting her personal honor and respect for each county's traditions and cultures. That is why having miniature representations of her clothing and the jewels she selected to create her ensembles is like owning, not her, but the impact she made upon History...and upon each of US who still love her.
 
  I think that is why having these dolls, wearing really true-to-life replicas of her carefully planned and crafted dress ensembles, is still so meaningful to so many people the world over. A friend of mine in Australia put it so well when she wrote me that she wanted her Diana dolls so that she could tell her little daughter one day that even Today, there still can be REAL Princesses whose work and joy in helping others can still bring joy to our hearts!

  Thus, Princess Diana's Work continues.

  Well, now you know what I know. There are other guides which will tell you more. But at least I have added something  ( I hope!) which may prove for a happier experience for Diana doll collectors!