What is the difference between the Paying Subscriber figure in Subscriber Retention and the New Subscriber figure in the Subscribers report?

You may have noticed that the total of Paying Subscribers within the Subscriber Retention report is higher or lower than the total of NEW Subscribers in the Subscriber report. What gives? 

The discrepancy between both dashboards stems from the differences in which type of subscriptions they include in their calculations. 

The Paying Subscribers figure in the Subscriber Retention report includes reactivations, but does NOT include $0 subscriptions or trial subscriptions. 

The New Subscriber figure in the Subscriber report does NOT include reactivations, but DOES include $0 subscriptions and trial subscriptions. The Subscriber dashboard splits New and Reactivation ('Returning') figures into separate columns.