There are cases where we overwrite the PlanCacheEntry stored in the cache, creating a new entry with a new "timeOfCreation". This means that the output of planCacheListPlans and $planCacheStats may be confusing. For example, when an inactive cache entry transitions to active, it will get a new "timeOfCreation" value.

See here:

https://github.com/mongodb/mongo/blob/7bc9953a256c1fab8b772812e712b909fefc4535/src/mongo/db/query/plan_cache.cpp#L776-L787