Interestingly pages 9 & 10 of the MACR notes thea/c serial number the a/c Group marking the a/c letter "L" and even the colour "yellow". However no mention of any other letters are noted.
Raises the question as to whether the Squadron letters were actually carried on the a/c ?
As I noted earlier this a/c seems to have only been used by the 305th BG, so may well have moved between its Squadrons ?
http://www.americanairmuseum.com/aircraft/5559