I've found this and I thought I might share...
Transmission identification codes start with a "T" and an example would be:
TY856WB1AA
"T" = transmission code
"Y" = that it is a manual awd gearbox
"85" = the transmission classification...in the case of manual gearboxes this number indicates the gear shaft spacing in millimeters. 6-speed transmissions use an 85mm shaft spacing while the current generation of 5-speed transmissions use a 75mm shaft spacing.
"6" = some reference to the transmission case. "6" is used for 6-speeds, "4" is used for 8-bolt 5-speeds, "2" for 4-bolt Impreza 5-speeds, "5" for Forester 8-bolt 5-speeds, "3" for 4-bolt Forester 5-speeds, and "7" for some Legacy turbo 8-bolt 5-speeds.
"W" = transmission specification. "W" is 6-speed, "V" is 5-speed, "Z" = AT with MPT, "Y" = AT with VTD, etc.
"B1AA" = indicates various details about the equipment such as center diff. type, front LSD, etc. and also about minor production changes.