Mustang in France in September 1942?

Umm...

8 Bomber Command, a US unit first flew missions in B-17s on August 17th, over Germany. But they didn't get escorted by P-51s.

The Allies bombing of the Renault factory in the Paris area in Sep 1942 led to the event described in my original post.  I haven't found any information about such bombing escorted by the P-51's.  I'd say 99.99% of the readers wouldn't bother with or realize historic inaccuracies of the novel, but I am not one of them

Mustang I's made their combat debut over Dieppe in August 1942 with the RAF. Now you could put a Yank in the RAF in one of the Army Co Operation Squadrons the flew the Allison Mustangs and get a plausible plot at that point...

Sounds like a book I read that described the afternoon sky in May as a  winter sky...

Well, considering that the conditions for the Normandy Invasion is June were described as being "from a meteorological standpoint resembling mid winter" that is a possibility.

Real life always has something to make you look twice and say, 'is this for real?'

Well yeah !

That's why " LIFE '" can kick you in the butt when you least expect it .