I don't know all the ins and outs.   Maybe FJ can answer your questions?   The final product of course is what is important, and that is the wafer which contains many (thousands?) of the product - VCSELs.   That is my understanding.   Of course in between there is the matter of growing the epitaxial substance on the wafers, and from my understanding, that is a critical and complicated matter.  FJ. highlighted that a couple of posts ago.

Again, please enlighten if assumptions about the VCSEL are wrong.