Well, let's see ....

UL lists the cord.

UL lists the plugs for placing on the cords.

Put them together, as intended.... sure, the assembly is not UL listed - but that's a distinction without a difference. UL certainly has no problem with connecting the cord to the cable. That is exactly the circumstance for which the plug was evaluated. There is absolutely no code, or listing, issue with your assembling something, using materials as intended, in a manner that simulates a manufactured product.

To try to twist words and say otherwise would lead us to conclude that the plugs can never be used, for anything, because the specific 'assembly' is not listed. That's an insane extension of "logic."