[tomazio]

This is more common than you might otherwise think. I've worked at multiple companies that have multiple systems/sources of truth for various reasons. One example of that is my current company has stored and handled all its transactional data in a legacy point of sale system from the early 90s. They decided to upgrade to a modern ERP system a couple years ago, but it takes a while to fully implement and roll over to a new source system. Especially in a high transaction system that cannot go down otherwise the company will start losing a lot of money. Thus its being incrementally rolled out, resulting in both systems running together and being read and written to simultaneously.