Steve Jones susses out a problem:
I had a customer that was looking to document a restore that had occurred on one of their systems and didn’t see it. They had concerns about SQL Server accurately tracking history across time and noted they hadn’t cleaned any history.
We dug through some of their instance jobs and found one that ran sp_delete_backuphistory. The person didn’t realize this removes restore history as well. This post talks a bit about how this works.
Read on for the full story.