Below is from some correspondence with Bob Hoskinson who flew in Ray's Bombing Group. It explains that the plane "Red O" may not have necessarily been the only aircraft that Ray and his crew flew.
Even though the crew was flying in this aircraft on the day they were lost doesn't mean that this was "their aircraft" or that it was the plane they normally flew. By the time they were lost, for the most part, crews flew whatever aircraft was available on the day they were scheduled for a mission. An example would be like our crew. We took an a/c from Langley Field, Va to Gioia del Colle, Italy. Upon arrival we were relieved of the a/c and it was sent to the 484th BG at Torreto, while we were shipped to the 464th BG at Pantanella. We flew 32 sorties in 27 different B24s. You checked the "Mission" board each afternoon to see if your "crew" was on the listing, and if I remember correctly, you found out what aircraft you would be flying when you attended briefing the next AM.
I think that when the group was originally assembled, perhaps each crew was assigned a particular a/c, but as time went by and aircraft and crews were lost they had to discontinue the practice. You might be assigned to an aircraft, but on a day you were not flying her, someone else had to. If that crew / aircraft was lost then your next mission would have to be on whatever was available. Later crews arriving at Pantanella were called "Replacement Crews" and never assigned to an aircraft.
464th BG, 778th BS
More information on Ray's crew can be found here http://ancientlights.org/familyveteransofwwii.html. Staff Sergeant John ("Jack") T. Dempsey was part of the "original crew" that flew with Ray, Bob, and Bill. Other "original crew" included ball-turret gunner, Fred “Cookie” Cook, tail-gunner Cornell (Corny) Fanero, flight engineer Sergeant Clarence “Red” Eudaily waist gunners, Jimmy Wright and John Lynch, plus bombardier Lt. Denny Wales. Only Ray, Bob, and Bill were aboard the plane when it went down in Oct 1944. Some of these original crew had perished in previous missions.