Yes, no one else has reported repeating my steps with Galerie, but it seems to me that posts 3, 9, 13, and 23 of that thread mention other APUGers being able to change the contrast of some graded papers using enlarger filtration. IC, I would be happy to send you a sample of that old paper, since I no longer use it, if you would like to check my results, as long as you are interested. I would also be happy to print a step wedge for a more objective comparison. Personally, I no longer use those papers, so the results would be more of an interest to me to satisfy my curiosity rather than to achieve a specific goal.
I just wonder if that paper was actually multigrade paper and not manufactured as single grade.