This article applies to all JSDR software versions.
When the JetStream DR upgrade has been started from the MSA appliance by running the command js_upgrade.py upgrade -v it creates a file "last_upgrade.log" under /tmp which lists details of the upgrade.
Upgrade command can be run with the -v option to see more description.
Reference: The below KB is the reference for MSA upgrade steps.
Upgrade JetStream Management Server Appliance (MSA)