According to this fishing website https://www.thai-fishing.com/fish-species-giant-featherback/ if its to be believed it seems like they are widespread but if anything it could also be confusion on that its actually a regular clownknife with little to no spots on it.2011 said least concern, 2019 says extinct. Trying to dig up the exact research that led to the conclusion.
I can imagine. Phylogenetics is still relatively new, but could help sort out the different species.