By surviving 35 bombing missions in a B-17, Rex Shearer and crew joined an exclusive club. http://ww2thebigone.com/2016/07/11/a-lucky-bastard
The RAF had the same issue. here is a book about a Lancaster crew which survived a tour of duty and there is a second book Mosquito Victory about the Pilot's second tour https://www.amazon.co.uk/Lancaster-Target-Jack-Currie/dp/0907579280 Pathfinder Lancaster Bomber crews flew a 45 mission tour