My opinion, based only on my experience with PCC adjustments.
Almost every + PCC adjustment I’ve seen has come in tournament play. Not all, but most. I think there are numerous reasons for that, and I’m sure that we can all figure those out pretty easily.
Minus adjustments have been much more rare events, though they seem to have become a bit more frequent in 2024; I currently have two among my 20 scores, both on my home course and both in “casual” rounds.
I think it’s at least possible that minus adjustments might have to do with summer? I’d attribute this mostly to the ball flying farther, and rolling out more on firm turf so that the course plays shorter, and maybe MUCH shorter. I’m 20-30 yds longer off the tee right now than I am most of the rest of the year. Hitting two or three less clubs into greens on par 4s and 5s makes a huge difference; more GIRs, better misses, etc. Add to that longer days and more practice, and lower scores follow.
As an aside, in CGA interclub competitions, you play off your 12 month low index. It turns out that almost everyone has their 12 month low in the late summer or early fall. Probably not coincidence…
So not really a course rating issue; rather it’s perhaps a different golf course than the one that was rated. And that WILL change when the weather gets cooler and the course gets softer.