I don’t think anything is stopping you buying a second hand / 3rd party module online. It just needs to be physically compatible with your particular generation of hardware.
Again I have no proof, but there must be reasons he claims they have to be blank NANDs
If you are building new SSDs, it makes sense to be certain that used NAND chips aren't slipping into your supply chain.
They do have a limited number of write cycles that they are good for, after all.