I’m curious if anyone on here uses a densitometer when testing or if everyone is eyeballing it off of scans?
I’ve been having a similar issue, not that it’s really an issue if you test for it, for the last year or so with XTOL (Kodak and the eco pro variant). Developing with XTOL 1+1 @ 20°C with inversion agitation every 30s for 400TX in 35mm requires a time of 13m30s to achieve a 1.25 range from zone I thru zone VIII. My base fog is 0.19, I is 0.29, and VIII reads 1.57 (close enough to my 1.25 target). This is considerably longer than the data sheet recommends, but the curves essentially match my old tests (2020) which were done at 10m to achieve the same range. Grain is similar and outside of taking longer everything is great.
I go through a full 5L bag of XTOL every month and XTOL has been this way since at least last summer. I changed darkrooms recently before that and assumed it was just something in the new water, but since I work out new times when I change location or chemistry it didn’t bite me.
Totally understand OP not wanting to test all of the different film stocks, but if you were at 10m and now you’re at 13m30s like me, you could try one other film at 35% longer than your old times and see if it’s on target. If so, you’re probably fine to use that time formula for all other films.