To continue your analogy:
Amphastar uses techniques that infringe MNTA's patents to demonstrate sameness, and using these techniques, they get approval. But they also show that if they monitor their 7 (non-infringing) elves closely, they always have sameness, and going forward they manufacture using these 7 elves only.
Possibly, but very unclear and I personally doubt it would fly. The problem is that you now gave a second level of indirection in establishing "sameness". I suspect the FDA would want to see some level of QA that directly establishes the sameness of the product.