sorry there is no report available at the SMA to report on this activity, even I also think this could be helpfull.
I am currently checking if such information could be made available when uploading raw data of the ESA/SMA to a SIEM.
Searching for "ISQ Released Message" or "released from quarantine" & "manual" in mail_logs would allow you to count and identify such messages in a SIEM. The SMA re-inserts such messages back to the ESA so you would need to search the ESA logs for such messages.
A document describing the release messages can be found here: