Hi,
I did some research on serial numbers for the GT Cyclone (1991)/Psyclone (1992-99).
Here is what I found:
Edit: update on 2012/09/28
a) "GTL"
GTL 9114 - Cyclone (black), model year 1991, 18 inch (U-Brake)
GTL 9120 - Cyclone (yellow), model year 1991, 16 inch (U-Brake)
GTL 9146 - Cyclone (yellow), model year 1991, 20 inch (U-Brake)
GTL 9268 - Psyclone (yellow), model year 1992, 18 inch (U-Brake, Groove Tube)
b) "P"
94P45 - Psyclone, model year 1994, 16 inch (Canti, Groove Tube)
94P124 - Psyclone, model year 1994, 18inch (Canti, Groove Tube, no replaceable mech hanger)
94P196 - Psyclone, model year 1994 (Canti, Groove Tube)
95P01 - Psyclone (black), original decals 1996, Groove Tube -> frame probably still model year 1995
96P025 - Psyclone (blue), model year 1996, 18inch (Canti, no Groove Tube)
96P120 - Psyclone (black), model year 1996, 18 inch (Canti, no Groove Tube)
96P193 - Psyclone (TeamScream), model year 1996, 19inch (Canti, no Groove Tube)
97P018 - Psyclone, model year 1997 (V-Brake, TT OX Gold)
97P183 - Psyclone (red), model year 1997, 19 inch (V-Brake, no Groove Tube)
98P069 - Psyclone (blue) modelyear 1998, 18 inch (V-Brake, no Groove Tube, Reynolds 853)
99P009 - Psyclone (white), model year 1999 (V-Brake, no Groove Tube)
GTL probably stands for GT Longmont, i.e. the factory where they were produced (brazed). L is definiately not the frame size, as all frame sizes use GTL.
"P" stands for Psyclone obviously.
The first two digits are the year of production.
The last digits are running numbers, not the week of production. However, regarding the GTL-numbers I am still unsure whether the running numbers start over every year or run through the years. If the number of the 1994 and 1999 Psyclone mentioned is correct, at least the "p"-models started new every year.
More serial numbes would help solving this mystery and will also give us a clue of how little frames were made. (Sadly, I cannot contribute as my 92 Psyclone does not have a serial number; it was probabaly lost (only a sticker under the bottom bracket in some years)).
Thanks for your help!
Maybe we can start a list comparible with the Xizang.
I did some research on serial numbers for the GT Cyclone (1991)/Psyclone (1992-99).
Here is what I found:
Edit: update on 2012/09/28
a) "GTL"
GTL 9114 - Cyclone (black), model year 1991, 18 inch (U-Brake)
GTL 9120 - Cyclone (yellow), model year 1991, 16 inch (U-Brake)
GTL 9146 - Cyclone (yellow), model year 1991, 20 inch (U-Brake)
GTL 9268 - Psyclone (yellow), model year 1992, 18 inch (U-Brake, Groove Tube)
b) "P"
94P45 - Psyclone, model year 1994, 16 inch (Canti, Groove Tube)
94P124 - Psyclone, model year 1994, 18inch (Canti, Groove Tube, no replaceable mech hanger)
94P196 - Psyclone, model year 1994 (Canti, Groove Tube)
95P01 - Psyclone (black), original decals 1996, Groove Tube -> frame probably still model year 1995
96P025 - Psyclone (blue), model year 1996, 18inch (Canti, no Groove Tube)
96P120 - Psyclone (black), model year 1996, 18 inch (Canti, no Groove Tube)
96P193 - Psyclone (TeamScream), model year 1996, 19inch (Canti, no Groove Tube)
97P018 - Psyclone, model year 1997 (V-Brake, TT OX Gold)
97P183 - Psyclone (red), model year 1997, 19 inch (V-Brake, no Groove Tube)
98P069 - Psyclone (blue) modelyear 1998, 18 inch (V-Brake, no Groove Tube, Reynolds 853)
99P009 - Psyclone (white), model year 1999 (V-Brake, no Groove Tube)
GTL probably stands for GT Longmont, i.e. the factory where they were produced (brazed). L is definiately not the frame size, as all frame sizes use GTL.
"P" stands for Psyclone obviously.
The first two digits are the year of production.
The last digits are running numbers, not the week of production. However, regarding the GTL-numbers I am still unsure whether the running numbers start over every year or run through the years. If the number of the 1994 and 1999 Psyclone mentioned is correct, at least the "p"-models started new every year.
More serial numbes would help solving this mystery and will also give us a clue of how little frames were made. (Sadly, I cannot contribute as my 92 Psyclone does not have a serial number; it was probabaly lost (only a sticker under the bottom bracket in some years)).
Thanks for your help!
Maybe we can start a list comparible with the Xizang. 
