I have an aviation historian/writer in England, Mike Jerram, currently looking for that logbook--not the actual logbook, of course, but some record of what's in it.
Everything I've ever seen in print that credits Grumman with having based its Bearcat on the FW-190 _specifically_ refers to Bob Hall and Bud Gillies having flown the airplane that the RAE had in "early 1943" (or "September 1943," but that makes no sense, as explained above). Nobody has ever breathed a word about the opinions of AAF, RAF, Luftwaffe or other pilots who might have flown it. If they did fly it, Grumman was not about to take their advice and only their advice.
If they did read reports from Wright Field, let's say, at most it would move them to decide to also get their hands on a -190.