It's unsurprising that the B-17 wreckage was found, by the 1945 patrol and others, at the B-17 crash site.
We have no way of knowing when the secret treasure map was embellished with the Electra data requested from the Americans, but there's a pretty good clue in the date: 24/5/45. The date of the patrol's discovery of the wreckage at the B-17 crash site was 17/04/45.
Occam's Razor makes it pretty clear that the wreckage in the vicinity of the B-17 crash site is that of a B-17 and that the information received from the Americans on the 24th of May was transcribed onto a map's border on that date.