Only know by ones I've seen in person and pics on-line. (as on this thread) I always wondered if where they 'lived' had influence - like were they mostly in a hot/cold environment as heat and cold has affect on thick coatings. All coatings are elastic to one degree or another, so the thinner the coating the less tectonic shifts occur as it moves. The already thin nitro finishes from the 50's-60's got thinner over the decades adding to their fragility. The coating 'shrinks'.
Optimally the varnish used on violin/cello/double basses is only there to seal and protect the wood and their formulas were very coveted secrets. Much debate goes into solid body basses concerning the tone potential of one slab of wood over another. It's far less critical than for an acoustic instrument, but can not be discounted - the wood (what type, density, age/dryness, overall form/shape/thickness, chambering, layering AND coating) makes a tone difference. So these very hard very thick finishes are like putting a coating like that on strings - I've never done it but I'm quite certain it will deaden the potential of the strings. Everyone and their brother stripped their finishes off in the late 60's/early 70's. (including me on my 3 yrs old EB-3) Part of that was the 'return to nature' (natural wood) mentality of that era, but it was also to free the wood for maximum tone potential. So there's 2 camps - those who want their flawless perfect new finish to last forever and those who realize that the 'perfection' they seek is in the tone dept, not the cosmetic dept. Every super distressed bass over these pages was very played meaning it sounded great and got better over the years because it was played a lot. Seems like a safe bet anyway.