Unlocking seats are not that rare
Re the above highlighted quote, I often wonder if Pprune readers have ever noticed that flying schools operating Cessna singles, often fail to mention to students that the Cessna POH manufacturers Before Landing Checklist, includes as the first item "Seats Secure". Yet it is a vital flight safety check. But then, it is not unknown for flying schools to design their own checklists which are often at variance with the manufacturer's published checklist for the type.