ORIGINAL: timtom
As far as I can tell, the vanilla Bangor/Bathurst MSW and its 1/43 upgrade are identical. the screenshots below are from scn.154, but scn.15 is the same.
Q1: Am I missing something?
No, looks like a problem.
Q2: If not, are there any reason I can't free up the upgrade slot and create a separate Bathurst class (for cosmetic reasons)?
You certainly can use the slot but I'd recommend keeping and correcting the upgrade. Use another slot.
Q3: Are there any RN/RAN experts out there who can tell whether there was in fact any difference between the the Bangor and the Bathurst?
Bangors were Royal Navy minesweepers with various types of propulsion (diesel, turbine, reciprocating). Some went to India and Canada.
Bathurst was an Australian variant of the Bangor, slightly enlarged for Pacific operations. Some were built for India but 20 ordered for the RN were used by the RAN during the war.
Q4: And now for something entirely different: Is there any way of assigning squadrons with "reserve" aircraft as opposed to ready/damaged?
No