I just loaded up our database backup from October 1 (three weeks ago) and compared it to the live database. Nothing has decreased. You've done 37 validated 321 jobs and 22 validated PPS sieve jobs between then and now. In the October 1 numbers, you had never done any PPS Sieve jobs.
Just to be certain, I then loaded the June 1 backup. Between June and October you completed 2 Woodall, 53 Cullen, 21 321, 681 SGS, 1 SoB and 78 TRP LLR jobs. None of your numbers decreased. You had not done any PPS sieving as of then, either.
You've never done anything that gives PSA credits, either manual sieving or PRPNet jobs. Here's your last last 40 days of PrimeGrid scores, as per boincstats.com. I'm not sure what you're remembering, but nothing has been deleted or decreased as far as I can tell.