Netflow Analyzer v9.6 - Database Cleanup

Over the last several months, Netflow exporting devices (ie. Routers) have been sending our collector data from an incorrect interface. After making the correction and sourcing the data from another IP (but same device), the device / data resides in our NFA dashboard but the ifIndex's are grey'ed out (no longer collecting data).

Also, some routers after they were rebooted, started sending NF data using another ifIndex ID (we've since made the correction on the router), but that data also still resides within dashboard.

I've configured some devices within NFA to be either unmanaged interfaces or deleted.

My understanding is that they don't really get deleted in the database until purged using SQL statements. Is that correct?

Is it good practice to cleanup the database every few months and is there a tool to simplify the purging of old/unused records?