Nice Job!

GM has its own internal codes - for most recent models, see http://www3.sympatico.ca/tedkrygier/future.htm (be careful about 2004+ models, some things have changed since this was written)

Also of interest:

http://findarticles.com/p/articles/mi_m0KJI/is_2_114/ai_83037290/pg_2

We could put the platform as chassis-code, as we do not have any code to use for these cars usually (this field having been made mostly for Japanese and European cars, cf the W-code and E-code of Mercedes and BMW)

I have been identifing GM vehicles at imcdb.org website with GM platform series. Should we use the platform series as part of vehicle category? Do you already have the vehicle series in the database field? Rebuttal?

Robert