Excuse my German ignorance, but my understanding of how it works here is that unless the transfer is notarized, logged and recorded with the local authority, there has not been a legal transfer. So, by that definition of land ownership, no "events outside of its jurisdiction" can take place. Any such agreements become binding only upon their verified registration. A notary is responsible not only for confirming the transfer but also as independent consultant so neither party gets seriously ripped off. (And if they didn't, they would be in serious liability trouble.)
The "share of the database" is managed and owned by the local government, but its records are available all across Germany for authorities to look up. The vector database of lots is public, and there are procedures to request access to ownership documents for various purposes. The procedure is that when you want to buy a certain property, the owner confirms that you have permission to get the official record directly from the land registry, which then become the basis for any serious negotiations as what is recorded there is in fact the single source of truth.