Another small point worth considering - the average RAF squadron normally had around 24 operational pilots, and (on paper) 18 aircraft on strength, with operational strength supposedly at 12 aircraft. From this you will see that each aircraft would be used by more than one pilot.
A particular aircraft was not generally assigned to a particular pilot, although in many cases, a pilot would try to use the same aircraft whenever possible, with seniority in rank and experience having preference.
The only real way to determine who flew what, is by access to the Pilot's Log Book, in the hope that the information is recorded, or, in some cases, the Squadron Operations Record Book. However, not all pilots (or other aircrew) completed the Log Book details regarding the aircraft in full, with serial number and individual code letter. A Log Book might just show, for example, the last three digits of the serial, or just the individual code letter. The ORB might not record any of these details!
If you are able to determine a serial number of a particular aircraft flown on a particular day, then it might be possible to trace the individual letter from the Aircraft Movement Card, but the letter was rarely included, as it could change with service requirements, as well as the aircraft being moved between other units. Likewise with just an individual code letter (if the serial is not shown in a Log Book) - often the only way to tie-in the two is by photographic evidence.
Welcome to the frustrating world of research !!