I just created a new site for someone and they went in to edit the page defaults and create some new pages, etc. -- I don't know what exactly happened but now the "Defaults" button is missing from the "Page Types" dashboard page (see attached screenshot). I checked the database and there is NO record with isTemplate=1 (but I know it was there at some point because I created it before handing it off to the site owner). I checked the Collections table for a record with a NULL handle, but there are none. I then checked the CollectionVersions table for a record with a cID that doesn't exist in the Collections table, and there are none.

How could a page template have been deleted entirely from the site, without the old version even remaining?

Thanks for whatever insights you may have.