Due to a firewall issue, I needed to see if an update to PANOS was related to a change in behaviour. I wasn’t sure exactly when the firewall had been upgraded. Searching through the system logs did not seem to show PANOS version changes. Finally I found a mention in a support forum of debug swm history. In short:

debug swm history | match 'install panos'

Will give you the history of upgrades. In this case from a test firewall:

Software History

You can see more info here

I can’t find the original support forum link to include.