There's Paul Mulcahy's reference pages: http://www.pmulcahy.com/best_stuff_that ... r_were.htm
(that includes a lot of stuff that's not in any of the GDW books, but some that was!)
A quick skim and my own personal brain (which is probably wrong in a few cases) says this:
HMMWV Fire Support Vehicle - don't believe this ever existed, even as a prototype, but it and things like it WOULD be an extremely likely battlefield modification
LAV-75 - only ever prototypes and not as presented here
M1A2 Giraffe - I doubt this ever even made it off the drawing board, at least in the 1980s. Certainly was never fielded.
M691 Diana - existed, but was never adopted
M990 ADA - T2K seemed obsessed with giving the US Army AAA capability that it never went forward with!
M917 ADATS - the ADATS system existed, but in US testing was always on a M113 chassis I believe, and never adopted.
M920 Hellfire - pretty sure this is a total fabrication
M757 Blazer - likewise.
M975 Roland - prototype only
The Soviet stuff gets even weirder, because the authors presumably had very little actual info to go on at the time:
T-74 - presumably this is just a T-80
T-86 - nah
T-90 - extra nah (a T-90 does of course exist now, but is in practice just a continuously upgraded T-72 and nothing revolutionary like a remote turret!)
M-81 - also nah
ZSU-30-6 - exists, but the details are wrong and ignore the missiles, etc. 2K22 Tunguska
BMP series -- Twilight is the only source I've ever seen that, for whatever reason, calls these "BMP-A" and "B" and "C" rather than BMP-1, BMP-2, etc.Their version of the BMP-3 significantly underestimates it
BRDM-3 - actually based of a BTR-80A, for some reason. And never adopted by Russia.
BT-76 - fictional, I think?
Further, all of these games miss the complexity of actual Soviet naming/upgrade conventions. There are multiple generations of pretty much all of their vehicles. A T-72B3 is a different beast entirely from a T-72A, for instance. T-80UM is significantly tougher and more advanced than a T-80, etc.