Primary Sources for Ptolemaic Egypt

[MeinPanzer]

I thought it was a requirement of a primary source that it had to be witnessed first-hand, or at least be contemporary. Not like those writing centuries later, and from the writings of others.

That is a primary source as well in the context of ancient history. If an author drew on contemporary sources, then his writings are considered a primary source.

If you see divisions in the bibliographies of articles on ancient history, you almost always see ancient authors of any sort listed as primary sources and modern critical literature listed as secondary sources.