A "? " or set of brackets, [ ], around a date of correspondence indicates that an exact date could not be located within the correspondence. A " Inc." marking on a file folder denotes an incomplete correspondence where a page or portion of the correspondence is not included in the collection, which often leads to an uncertain date. The abbreviation of " P " on a file folder indicates either a photograph or a piece of published material was included in the correspondence by the sender. In either the front or back top corner of each letter, the cities from which the correspondence was written and sent are denoted from the postmarks and envelopes accompanying the correspondence.