I have generally had good results when asking about details of a large codebase. Having tests keeps everyone honest. It may not always get the right answer on the first try and sometimes only does a partial job (find all other instances like the fix you just made).
Things go wrong when working with new external APIs as the AI will have read pote tial fixes that were never implemented. I have found that asking to see the documentation for a feature is a good way to avoid guesses.
Developer Rants 