The J. H. STOLOW mark and variations thereof are not as meaningful as you might think for several reasons:
-- there is another school of thought that believes the family members were businessmen, and they marked their stamps primarily for business purposes, not because they were experts in that field (in other words, it was a mark that primarily signified a money back guarantee, rather than meaning they had researched it in depth and found it to be genuine)
-- their marks are widely forged; in fact, I'm not at all convinced the mark you have is genuine -- the letters are way too thick for the specific J. H. STOLOW mark, and I've not seen it in that ink color (what expert uses reddish ink?)
The authenticity of the stamp must be determined independent of the STOLOW mark.
Nice stamp, and thanks for the nice big picture of the stamp!

k