Let's be real, a lot of organizations never actually finish that R&D phase, and just continue iterating on their prototypes, and try to untangle the spaghetti for years.

I recently had to rewrite a part of such a prototype that had 15 years of development on it, which was a massive headache. One of the most useful things I used LLMs for was asking it to compare the rewritten functionality with the old one, and find potential differences. While I was busy refactoring and redesigning the underlying architecture, I then sometimes was pinged by the LLM to investigate a potential difference. It sometimes included false positives, but it did help me spot small details that otherwise would have taken quite a while of debugging.