jeffb,
First, welcome aboard our Prince of Threads ! (you must not apologise for your "lengthy Post"; every word may trigger off others' reminiscences; it is exactly what this Forum is all about).
In amplification of Petet's reply, I must stress the importance of his words "may" in the interpretation of mere letters and figures in the "Duty" column of your Father's Logbook.
Although all my American training entries are descriptive, the subsequent RAF (AFU plus OTU) ones carry something like "Ex 18A", which mean nothing to me now, as I have no Schedule of the Exercises. I believe this was common in all our flying (inc Nav and Bomb Aimer, etc) schools of the period. Yet someone may yet remember and be able to help you out.
(From Wiki and "World War II Today"): "A total of 95 aircraft were lost" (on the Nuremberg raid) – "at 11.9% the highest rate for Bomber Command for the whole war".
Cheers, Danny.