At one point I had sources for information about lens specifications for lenses of various manufacturers. But I can't now find anything which tells me the separation of the principal points for different lenses that I own. Some websites that I used previously no longer seem to exist.

These are
Rodenstock 150 mm Sironar-S, 90 mm and 75 mm Grandagon-M
Fuji 300 mm compact
Nikon 210 mm.

I think I do need the separation of the principal points to determine where to measure subject distance from if I know the rear flange focal length which tells me the position of the rear principal point. In principle, I think I could measure the distance from the flange to the front focal point by reversing the lens and focusing at infinity, but I would prefer to look it up somewhere if I can