This appeared after I had opened a file, edited it, then decided to do a "Save As..."
The system had been Auto Saving my edits to the original file.
As a result, the edit history was lost when I saved it as a new file.
This mistake may have been repeated if it wasn't for their tip.
It would have been stronger if there was an option to roll back to the opened state (no edits) and load the edits into the new file. Maybe that feature is in their backlog.
Learn more link opens this page:
https://support.office.com/en-us/article/save-a-copy-before-editing-to-prevent-changing-the-original-file-8aeabebe-952e-449b-b931-ae2b7568771b?wt.mc_id=SaveaCopy_AutoSaveUI_Mac&ui=en-US&rs=en-US&ad=US