Below is a response I got from Marketo Support:
1. I researched your question about the discrepancies in numbers in your RCA and Analytics reports. The discrepancy is explained by the fact that RCA and Analytics Reports measure those numbers in different ways. In RCA, the number always includes the overall numbers of instances of an email being delivered. E.g., if an email was delivered twice to the same lead, that will add as 2 counts in an RCA report. Also, it won't take into account activities such as Merge, so if an email was delivered to two leads that later got merged into one, it'll still count as two instances of an email being delivered. That's why in RCA reports, the overall number almost always will be slightly higher.
In Analytics report, the number stems from the first time that an email was delivered. E.g., if an email was delivered twice to the same lead, it will count as 1 in an Analytics Report.
In a regular Smart List, the count of leads will be based off the leads that are currently in the database. So, if a lead was deleted since the time that an email was sent, it won't show in the Smart List, however it will add to the number in an RCA report or in an Analytics report.