Close this as the details are very limited, and registry sync now has an idea if the registries are modded or not.

Ah ok, thats a neat idea, I will reopen this 👍

Thanks :)

If I recall correctly (and note, this was almost four years ago), this was supposed to be a feature where the untampered ID/object information of the registries as initialized by vanilla was cached and preserved. This would ensure that one can always roll back to this state to, say, try and connect to a vanilla server instance from a modpack which added some non-critical registry entries, or after trying to load a world which changed the ID/object ordering.

see also: #88