How to calculate average visitation in Altru??

Hello – I got a seemingly simple request from my museum team – what is average member visitation broken down by membership level for the past fiscal year, and for several pre-covid fiscal years. The goal is to see if, on average, the membership is used enough for visitation to pay for itself. Sounds easy enough but I have been on a 3 day downward spiral and have gotten no where. I realized that I can't look at sales orders because that excludes memberships with 0 orders. And then I realized that I can't really use fiscal year since memberships have rolling start and end dates so visit counts wouldn't be accurate unless it included that membership's entire period. Someone has to have a better way to calculate average visitation stats… Help!!