How are others using Success Plan completion % for reporting?

We usually have more than one success plan open for a customer. My challenge for reporting becomes what do I use as my overall complete number? If I only use active success plans then the CSM could be 50% of the way through his total success  plans (2 plans each with ten tasks, 9 complete in plan A and 1 complete in plan b). Then (s)he completes the final task for plan A and closes things, now their complete % drops to 10%. Conversely if I use non-active plans (closed) then once we have a large number of closed tasks, the open tasks will not move the needle much and 90% complete won't mean much. 

Thoughts?