The only genuine boards I am aware of are "new old stock" of Nanos, OpLinks, and Sparky2s from very specific sellers. Everything else (Revos, CC3Ds, other sellers Nanos, OpLinks, Sparky2s) is a clone.
Some educated guesses: The very best clones use the original board layout and may use high quality components; they would be equivalent to genuine boards. Some clones use the original board layout and lessor quality components including leaving some components out. Some use components that are known to be incompatible (e.g. baro issue). Some are new or different board layouts.
I have bought several clone Sparky2 boards, and they generally work well, except for the fixable baro issue in some cases,
I don't buy bare CC3D boards any more and sort of recommend that you don't either because the CC3D memory is full and doesn't get new features added although I would consider buying an aircraft prebuilt with a CC3D.