Running Sum Overcounting

Is there a way to stop a running sum from double counting a value that pulls into two separate rows? So only count it the first time it shows up?

For rows I’ve got Order Weeks Since Onsale and values I’ve got running sum (by category) for the number of unique Performance IDs.

It’s for our education bookings where our targets are done by number of performances. Usually it’s one order/constituent per performance but sometimes multiple schools share a performance. If they are booked in separate weeks then my totals are off/overcounted.