My (rather novice) understanding of U.S. Army Air Force (USAAF) practices during WWII (and afterwards in the U.S. Air Force) is that aircrews were assigned specific airplanes, and that if an aircrew's airplane was inoperable then its missions would typically have been assigned to a different aircrew with an operable airplane. Is my understanding wrong? If not wrong, then were these practices a matter of policy? Tradition? How often were they counteracted, and for what sorts of reasons?
I'm trying to learn as much as I can about this crash in October 1942. All USAAF records of said crash indicate that the airplane involved was a B-24D designated 41-23712 (nickname "Ambrose" [or "Ambros"]). Any related material you find in a cursory search of the internet regarding this crash is almost certainly already known to me. A letter dated 1993 indicates...
...retired M/Sgt. [name redacted] was a ground Crew Chief on one of the 330th.B.S. planes. He remembered Capt. Williams and told me that his regular plane was "AMBROSE" serial No 41-23712-R and was under repair and the only other plane available for their mission was, "READY TEDDY" serial No 41-23721, so that was the plane they crashed in.
This is supported by the pilot's daughter, who was given keys found with her father's body in the wreckage--those keys have a tag on them stamped with:
This is a surprise to me given my understanding described above. Hence this question.