Flow filters "Has not been in flow at any time" and "Has not been in flow in the last X days"

I have a post-purchase flow with the flow filter “Has not been in flow at any time” in order to prevent customers from re-entering the flow while it is still sending out e-mails.  But I do want customers to re-start the flow after it has ended (the flow covers around 6 months, by the way).

Since the "Has not been in flow at any time" trigger has a special way of working (it is obviously only checked ONCE at the beginning of the flow, and NOT at every step of the way, like normal flow filters), I am not sure how I could make that flow available again for returning customers (for another round of the same e-mails).

My initial idea was to change the flow filter to “Has not been in flow in the last 2 days” but I guess this would lead to skipped emails because this filter actually IS being checked before EVERY step of the flow - correct?

So … maybe someone could please quickly recap EXACTLY how the filters "Has not been in flow at any time" and "Has not been in flow in the last X days" work.

Thanks!