This is a great thread idea, but I think all this SN info is not very useful unless we associate it with specific, identifying attributes. Here are some ideas for future (and previous) posts:
- SN / MADE IN USA Stamping - Serial numbers and/or the alpha prefixes may be a key, and for some reason, some frames do not have MADE IN USA stamped in the BB shell.
Bike Size & Head Tube Length - I believe head tubes are shorter on newer years given size on older frames. Not sure what the year change was, but I have read that early models were not suspension corrected.
Head Tube Shape - Some 'Zangs (pre-1996 I believe) have a slightly thicker collar at the top and bottom of the headtube. Later models are straight.
Rear Brake Hanger - Newer models (starting perhaps 1996) have the ring welded to the seattube, earlier models have a welded cable stop.
Rear Dropouts - GT logos, plain, removable, etc. Not even sure how many options there are.
Cable Routing - Someone mentioned internal routing on a very early model. Different types or locations of barrels.
Stickers - Obviously not a good identifier unless there is some reason to believe they are original.
Photo - A simple photo of the frame could help with other attributes that I didn't think of here.
There may be others, but I think it's a good start.