This is a follow up ticket from SERVER-70025.

Currently we only count cache plan cache hits and misses, regardless of the query type. That is, we expect a plan for the given query to be in the cache, and as such can be recovered from the cache, or missed from the cache, and needs to be replanned.

However, there is a difference between "didn't use cache because there wasn't a cache entry" and "didn't use cache because this query is ineligible for caching". 

We may want to consider adding a third counter (in additional to "hits" and "misses") to account for this difference.