I seek clarification (if possible) with regards to the ranks of certain members of the crew.

Reference books list the following at the rank of Sgt.
However the CWGC, list them as :-

Wireless Op:
J/92361 P/O William Russell Karstens, RCAF, Age 22 +
Air Gunner (upper):
J/92914 P/O Donald Alexander Trott, RCAF, Age 19 +
Air Gunner (tail):
J/92476 P/O Thomas Bernard Tierney, RCAF, Age 22 +