Let me bet: Rebuilding from Jira email notifications. Yes, the diffs in the notifications.
Gray•Duffy, LLP Settles Two Massive International Data Loss Claims Arising From Computer Server Failures
Arc Touch, Inc. vs. Atlassian PTY, Ltd
http://m.grayduffylaw.com/?url=https%3A%2F%2Fgrayduffylaw.co...
https://www.theregister.com/2012/05/09/atlassian_cloud_stora...
In my limited experience these diffs can be missing information. I recently had to reconstruct an issue description using these email diffs after two people where editing the description at the same time and it was not 100% accurate, several lines were missing. Going to the 'history' tab on the issue I was able to get the missing lines however, if all you have are emails though you might be out of luck.