I read that first link; it stated that it is not USP. So either it is or it’s not :)
As for internal use, none will be for internal use so you can ignore that altogether.
All I can tell you is my personal experience from my limited research the specs for USP are tighter so you get a more consistent product. Certainly from experience the USP bottles I have contain a darker, thicker and smellier product…
As I said before, buy USP if you can otherwise non USP Lugol’s is far better than no Lugol’s.
BTW: I you had to depend on my scientific background we would stay stranded on the desolate Island