Hi @Steve ,
For Question 1, this is the date you create the Page.
For Question 2, by default, OneNote uses the date and time format specified in the Control Panel in Microsoft Windows.
For Question 3, if the page is emptied in Recycle Bin, you can also refer to this support article to check if you have any backup files in PC:
https://support.microsoft.com/en-us/office/recover-deleted-notes-32ed1036-74fd-4c21-bc28-033a486e6b14?ui=en-US&rs=en-US&ad=US
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