Hello, and thank you for using the Cisco Support Community.
If I understand your issue fully, you noted motion triggers in a 2521V camera log, but the archive footage was not retained in a motion archive on the VSMS server, so are looking for a way to see when the trigger arrived on the VSOM server.
Navigate to the VSOM Admin page. Under System > Events there exists a link for displaying Triggered Events. If the VSOM server received a motion trigger, it would be recorded in that event log.
I hope that helps,
Jim