What determines whether a GPU will be supported?

Does MOS whitelist the GPU chip itself or the configuration?

https://www.techpowerup.com/gpu-specs/?architecture=R500&sort=generation

There are many "different" chips but with same config of TMUs etc so effectively the same? OK, some differ with VRam being DDR, DDR2 or GDDR3 which I could understand could be an issue.

MOS says it supports:
ATI Radeon X1300 (no W3D)
ATI Radeon X1300 Pro (no W3D)
ATI Radeon X1550 (no W3D)
ATI Radeon X1600 (no W3D)
ATI Radeon X1600 Pro (no W3D)
ATI Radeon X1800 (no W3D)
ATI Radeon X1900 GT (no W3D)
ATI Radeon X1950 XT (no W3D)
ATI Radeon X1950 Pro (no W3D)

But
Radeon X1600 PRO & X1600 XT are same GPU, same memory type and size and same TMU etc config but X1600 XT isn't listed?

And ATI being ATI means there are MANY different configs of X1600 Pro (DDR2 etc) to add to confusion

Personally I am looking at a GDDR3 X1650 Pro to buy... its R535 but the config is same as "compatible" GPUs... No idea if it will work?