I think you're mixing up the R&D X-planes (there are lots: https://en.wikipedia.org/wiki/List_of_X-planes) with the actual aircraft, which isn't gonna have its first flight for years.

USAF plane naming is... odd. F-35, F-117, B-1/B-2/B-21. Not much rhyme or reason. It's very possible 47 was picked for Trump's benefit. Silly, but possible.