That's a bingo. It definitely wasn't primed. No staining or soft spots that I could find so what you suggested was exactly my plan.
In the "gift that keeps on giving" dept, I started this project because of some software drywall right on top of the shower/tub surround. When I started looking at it (i.e. cutting stuff out) I found out that the drywall was 1/2" too short and their solution was to run paper tape across the gap, mud it up, caulk the bottom, and call it a day. The caulk dried out and failed (20+ years old) and softened up the paper tape. I solved this bit using plaster of paris, though I still need to sand and paint.
Thanks everyone for your input, much appreciated!!!