Your first sentence has a typo, should read 42-52
585 not
858.
http://www.b24bestweb.com/section8-v2.htm
B-24H 42-52585, 465th Bomb Group, 783rd Bomb Sqdn, MACR 6751
http://www.783rd.org/index.html
Fold3 has the 37 page MACR available, but you'll need to join or start a trial membership.
https://www.fold3.com/search/#query=42-52585&t=95
Original Crews
http://www.783rd.org/History/OriginalFrames.html
This link shows who went MIA on July 19, 1944 and August 24, 1944. Trimingham went missing on Aug. 24, 1944.
http://www.783rd.org/History/CasualtiesFrames.html
It was not uncommon for an aircrew member to substitute on different aircraft during their tour of duty, due to mechanical issues, training, sickness, wounds or days off.
Example - Aircraft "A" gets hit by flak and cannot participate in the next days mission, even though all 10 aircrew members are scheduled to fly.
Aircraft "B" had one of its gunners injured from flak and cannot fly. A gunner from aircraft "A" would substitute on aircraft "B" for the next days mission.