I will allow a manager interference after a failed pin save on the same pin attempt sometimes. Not always. Maybe it's not realistic but this is wrestling and a lot can happen while the ref is going to start his count.
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If either is gonna definitely happen then I roll the managers distraction.
If that doesn't save the match then I roll managers interference - but only - if they have an actual interference chart (like say Kevin Sullivan's ROH manager card).
Otherwise if that doesn't save the match on that pin/sub attempt then I roll the pin save (if still applicable i.e. the offensive wrestler doesn't have to re-roll on offensive level 3 as a result of the interference attempt)
Once a manager has successfully distracted once and (provided they have their own interference chart) successfully interfered once, then the manager is done for the rest of the match.
And I only roll the pin saves when someone is definitely going to be pinned or submit.