re: I was told at some point that someone like Michelin was buying
them

I recall Vredestein as a part of B. F. Goodrich, which of course was
purchased by Michelin.  (The aircraft portion of BFG--brakes,
etc.--was spun off, I believe.)  Vredestein bicycle tires (!) are
available in USA but I have no experience with them.  It's hard to
believe these tires were ever anything special.  Rather, I think
quality in this industry is most directly proportional to investment
and it's hard to beat Michelin.  Personally, I always wanted to own a
set of Metzeler snow tires, which had blue tread. ('70s)