To play color commentator to Mr. Blaine's play-by-play announcer, there's only a marking requirement to certify compliance:
https://www.ecfr.gov/current/title-49/part-571/section-571.108#p-571.108(S6.)(S6.5)
That requirement to put a "DOT" marking on it is what, I think, causes all the confusion. The DOT does not play a role in verifying that compliance. They are reactive, not proactive (meaning, they investigate complaints/crashes via the NHTSA, which is part of the DOT.) People assume that the DOT approved it if that marker is there, but that's not at all the case.
Are we enjoying our day as an automotive engineer?