Good that you found a "fix" for the problem. I noticed you live in the mountains, and were able to raise the RH to 25%, you need higher RH to keep film from cupping. I live in the east and normal RH here is around 70%+ . Winter the humidity drops below that and I get cupping when drying film, then it flattens out. Shooting expired film has more effect on your film than humidity and especially developer choice, it stays in the cassette rolled tightly for too long. I would also think that the age of the film, having been subjected to many years of humidity cycles, even when frozen, that prior to processing and hardening the emulsion, it will leave the gelatin layer shrunken ever so slightly, that curl is inevitable.