> ... followed by howls of anguish from the rest of the business when it turns out they were relying on reports generated from a data warehouse which incorporat

> ... followed by howls of anguish from the rest of the business when it turns out they were relying on reports generated from a data warehouse which incorporated a copy of that MySQL database and was being populated by an undocumented, not-in-version-control cron script running on a PC under a long-departed team member's desk. Once you get to this point, there's no path forward. Either you have to making some breaking changes or your product is calcified at that point. If this is a real concern then you should be asking what you can do to keep from getting into that state, and the answer is encapsulating services in defined interfaces/boundaries that are small enough that the team understands everything going on in the critical database layer.