> isn't there always some authoritative source

yes there is, and that's why most blockchain projects that interact with the real world are doomed to fail.

Another classic exemple are those who wants to solve supply chain problems. To put it simply, the robustness or decentralisation of the database is not the reason why your inventory doesn't match what's in the warehouse. It's all human-related problem (eg. theft, losing shit, scanning the wrong item, being scammed by suppliers, etc.).