Question
Are Monthly Active Rows (MAR) counted for historical data in a priority-first sync?
Answer
Fivetran will count MAR for all the syncs running on the priority sync feature with the exception of the very first sync, including the ones that are fetching the backdated/historical data.
Please see the detailed Documentation here. No action is needed at your end.
Cause
Priority-first sync counts MAR for all the sync except the first one.