Ticket systems are quite ephemeral. I still have access to commit messages from the 90s (and I didn't work on the software at the time). I haven't been able to track the contents of the gnats bug tracker from those days.
And of course tickets can be private, so even if the data survived migration, you may not have access to it (principle of least privilege and all that).
if you've changed a function and are worried about the reason for the change not being tracked or disappearing, then add it as a comment, the commit message is not the place for this.
And of course tickets can be private, so even if the data survived migration, you may not have access to it (principle of least privilege and all that).