Modern enlarging lenses are optimized one or two stops down, and if any focus shift occurs it is likely
to be only one the first stop. But I don't know about old enlarging lenses or cheapo ones. And in my
own collection of enlarging and process lenses, only one lens exhibits any focus shift at all, at it's the
least expensive one of all, but still very usable a stop down. Some of the very best lenses are very
sharp wide open, but might have excess illumination falloff compared to stopped down. One just needs
to test the variable, which is quite simple to do in terms of basic characteristics.