The only situation I can think of where it's always safe is if the order that you apply changes to the state never matters:

- Each action increments or decrements a counter

- You have a log of timestamps of actions stored as a set

- etc.

If you can't model your changes to the data store as an unordered set of actions and have that materialize into state, you will have data loss.

Consider a scenario with three clients which each dispatch an action. If action 1 sets value X to true, action 2 sets it to true, and action 3 sets it to false, you have no way to know whether X should be true or false. Even with timestamps, unless you have a centralized writer you can't possibly know whether some/none/all of the timestamps that the clients used are accurate.

Truly a hard problem!