Instead of insisting that fine-tuning reliably adds new knowledge to an LLM, why not instead show some evidence of this claim. Per my links above, this is a notoriously challenging problem in ML.

Apart from these resources, let's think critically for a second. If the approach were viable at this point, then there would be tons of commercial solutions using fine-tuning instead of RAG for incorporating external knowledge in an LLM application. Can you find even one?