The more recent the news, the more valuable it was to editors, but choosing, compositing (arranging the metal type), and printing information from other sources took time. In order to speed up the printing process, editors of weekly or semi-weekly newspapers often composited text as they received it. You can see this in nineteenth-century newspapers in two ways.
The first is the Post Day, the boldface, often Gothic, lettering that declares Monday’s or Saturday’s Post. These informed the reader how recent, or fresh, the information below was.
The second was in small notices from the editors to his readers. For example, ‘There was nothing of interest in Saturday’s post’. Subjective though this assessment was, it let his or her readers know that the information they were receiving was the still the freshest possible, even if the Post Day was a few days old.
Post Days are different from Datelines in that they indicate when a newspaper or letter was received by that particular editor, rather than when that letter or newspaper was written or printed.