We are maintaining and extending a bunch (15 around) large ERP/data type projects which are over 20 years old with vibe coding. We have a very strict system to keep the LLMs in bounds, keeping to standard etc and we are feeling we are close to not having to read the code; we have over 2 months of not having to touch anything after review. I designed most of those projects 20-30 years ago; all have the same design principles which are well documented (by me) so the LLM just knows what to find where and what to do with it. These are large 'living' projects (many updates over decades).