Dating most Mongoose produced bikes is generally easy. A few different serial number patterns were used over the years beginning in 1975 with the first frames.

The first year or so the serial numbers were stamped in sequential order and a little hard to date exactly. Features of the frame design changed alot early too, so those most often give the clues for year built.

The most common and largest produced era was 1978 to 1985.

For the most part, frames from 1978 to 1981 were stamped as such.

CH9 123456

The C stands for Chattsworth [California] were the frame was made. The next letter is the month code.

A = January
B = February
C = March

And so on. This guideline aslo applies to Jag, Blue Max, Roger DeCoster, Super-X, Moto-Trac and perhaps a few others I'm forgetting that were all produced by the Mongoose umbrella of B.M.X. Products Inc. If a capital T is in front of or above the C that signifies a Team or 100% chromoly frame. Team Mongoose, Supergoose, Moosegoose, Team Minigoose all should have a T in this era.

The next number is the last number of the year produced.

8 = 1978
9 = 1979
0 = 1980

And so on. The rest of the serial numbers are sequential and mean nothing.

Sometime around 1981 production mover overseas and the date code system changed. From here the first letter is believed to mean nothing. Alot are M and some think thats for Mongoose, others think it's a month code still, I'm not sure. The second digit is the last number in the year produced. So an M2555767 would be a 1982 frame. This system continued until at least 1985 or later.

Several other design changes happened throughout this era of Mongoose frames. If you have any further questions let me know, sending some photos with lots of detail shots would be helpful if your stumped.