Is there any way of checking a past activation online via a callsign?
From SOTAdata, go to the activator roll of honour, find the callsign, select View Log, and find it in there.
To paraphrase Obi-wan Kenobi
“Use the database Luke!”
Several ways, search for the activator callsign in the honour rolls (pick association and year). Or back from the summit activation history. You can view things like this also on SOTL.as which has some different views.