While I am currently unaware of any such method to passively detect this without the exact card running the exact VBIOS in hand I am mighty curious if at the end of the day there's some stupid setting to force dithering on by default for certain GPUs with certain VBIOS's and that's what all this fuss with newer GPUs is about.
As I just said in another thread that would lend credence to this theory
However while my tests aren't entirely conclusive I have a certain RX 580 card that has dithering on by default which is even visible in the BIOS screen before any operating system driver would have relevance.