You can usually date the Aunt Martha's Embroidery transfers by looking at the envelope. 

1920's-1930's - Brown Paper envelope- Numo transfers (wax dots)
1940s - Blue & red envelope the has a feather edge on the left side with scattered stars
1950's - Blue & red envelope that has a blue-checked background
1960's - Blue & red envelope that has a yellow ribbon swirreled about
1970's - Pink & yellow checked envelope or just pink & yellow
1980's - Yellow envelope
1990's - Yellow envelope with the class of transfer color stripe across the top - red, green, black, white, or blue.
New/current - brighter yellow/gold envelope with 3 languages at the top of envelope.