[AndyMa]

There are all sorts of reasons for an aircraft to be recoded.
Some squadrons used different codes for different flights (eg first 13 letters for A Flt, second half of alphabet for B Flt). So a transfer between flights might trigger a code change.

Also, if an aircraft was damaged and taken out of the battle for a short period, a replacement aircraft might be delivered and take up the code, resulting in the original aircraft needing to be recoded when it re-entered service.