Good point, re: California-driven solvents. I don't know the answer. Like I said, I don't thin finishes except to thin spar varnish with naptha for top coating. The jugs of mineral spirits, acetone, and denatured alcohol I keep around are mainly employed as de-greasers and for mopping up epoxy squeeze out on glue joints and to de-oil oily woods such as teak and rosewood before gluing them.
And there are few other uses for thinners in finishes...
Back in the day when good oil was hard to come by a little thinner in oil made it easier to apply. But these days, thickened oil should be tossed.
