How fragile is the local data? Will it be preserved if I switch phones? What about past events that aren't on the current phone? What if I use two phones? This

How fragile is the local data? Will it be preserved if I switch phones? What about past events that aren't on the current phone? What if I use two phones? This takes a unified view and fragments it for spurious user privacy benefits (when we know Google is still collecting and holding all the information needed anyways).