I promised to report back:
I was charged $75 when checking my bag at the start of my trip at SRQ. I believe this is because it was a basic economy fare, but possibly because of the segment with AerLingus. We had only one bag to check in total. As it turned out, the bag was not put on the DUB-GVA segment, but fortunately, it was delivered to me the next day in Laussane.

On the return, all AA metal, there was no fee! So perhaps it all had to do with the partner segment. I will do my best to avoid that in the future.

Perhaps of note, my boarding pass listed me as Ruby status, so we were allowed to board the AerLingus flight at DUB ahead of other passengers.