If you allow A's state to lag behind it's own events
That's a mischaracterization. A's state is not lagging its emitted events; instead, A's state may have been changed at the time A's event is processed.
The "own events" was the faulty assumption. it's not always the same service that both emits the events, and is the place to go to over http for data. It "seems logical" to also build that store from listening to events, but it can cause issues as mentioned.
> when A's state lags or has moved on ahead of the event
That sounds like it can EITHER be ahead or behind. Specifically, I do not understand it as A's state can either lag OR be ahead, not that "lags" is a synonym for "moved ahead"