Yes, there is a difference in quality between manufacturers.
As far as I know, there is only one manufacturer offering the checkerboard blanks, and they are, generally good (not GREAT----good).
Even the absolute best manufacturers will have an occasional blank that is not perfect, but as resellers, we expect to have to replace one, once in a while. In the past two years, I have seen more "bad" blanks than I did in the preceding 2 decades. But, to be fair, I have had a lot more blanks pass through my hands at Exotics than I did when I was making pens. So, it could be the "law of larger numbers" or the quality control could be slipping, or we could be seeing more blanks from previously unknown makers (maybe they made them before, maybe they are just starting).
Pattern flaws, you should expect. Bubbles are a defect and the distributor should replace the blank.
But, that is a "business decision", not a law.
We replace them, Roy replaces them---both of us are active on IAP, those who just watch IAP, I can't speak for.
FWIW,
Ed