A lot of cutting work used to be carried out on what would nowadays be considered "inferior" quality blanks.
Producing any sort of blank was expensive and work intensive - they were all used, if at all possible.
It was simply because the technology and chemistry hadn't been refined the way they are now.
(

Very early on in collecting, my brother and his OH left an Irene Stevens vase sitting on a shelf - at a very, very desirable price - because it had a couple of small bubbles and bits of frit in it they decided it couldn't possibly be "right".)
Now, we know if there's a lot of work done on "inferior" blanks, it's because they're probably genuinely very old.