The Content page displays a list of all aircraft and newsletters added to the system. Newsletters are not stored long-term, but Aircraft are only deleted manually and only then if there are no flights associated.
If you cannot find the aircraft or newsletter in the list, you can narrow down the search using the Title field.
In the example above, you can see a newsletter that has been started but has not been sent (Status is "Unpublished"). This page is a simple way of finding a newsletter you started work on but did not finish.
Likewise, when an aircraft is made permanently unavailable, it will disappear from the list on the Aircraft tab, but you will still find it listed under Content. You could use this to view the log of an old aircraft that is no longer available for future bookings, or to re-activate an old aircraft in the system via its Availability tab.