I don't think the extra tape/vinyl was used in a manner of altering or modifying any shape or profile or contours of the bumper cover/valance/airdam/splitter, because that would have been noticed during pre-race inspection.
I don't think it's simply a piece of flat vinyl on a solid part of the fascia laying flush somewhere under the wrap. If teams didn't care about painting vs wrapping their cars in the past to gain a perceived aero advantage, or strategic vinyl/decal placement, or adding decals on the surface as opposed to being printed in the wrap, or any of that stuff back when they had legal choices.........I don't understand why they would suddenly care now.
Someone in the twitter comments mentioned the vinyl under the wrap may have been covering some holes. That might be why NASCAR and JGR specified CLEAR vinyl, but didn't explain exactly where it was positioned on "the lower corners" of the fascia. That would suggest JGR cut the wrap like they normally would wherever there's supposed to be a hole, but it was actually covered by the clear vinyl. If that's the case, where are these holes located? And it would somehow be inconspicuous enough to pass pre-race inspection? I'm not buying it.