That's not quite right. There are a lot of sound strategies for culling/merging/resolving CRDT state in-part or in-total depending on the use case and/or the topology of the system that interacts with the CRDT.
It's possible to construct a pathological case where it's impossible to soundly GC the CRDT state, and where you have to keep around an arbitrarily long list of per-agent updates or list of agents forever, but that shouldn't be the normative case.
It's possible to construct a pathological case where it's impossible to soundly GC the CRDT state, and where you have to keep around an arbitrarily long list of per-agent updates or list of agents forever, but that shouldn't be the normative case.