Is there a way to sort a PGN chess game by date and export the sorted games as a new PGN file?
I have not tried this myself, but there is a forum post on chess.com that has instructions on how to do this in SCID (http://www.chess.com/forum/view/help-support/sorting-a-pgn)
- Make an empty scid database
- Import your games
- Do database maintenance - Sort by date
- Export your databse to PGN
I am sure there are many programs that include this functionality. I would be surprised if SCID (http://scid.sourceforge.net/) did not have it. There should be one or more online services that provide this function. In the end of the day, you can write your own script in e.g. Python that does this easily and nicely. The trick is that some games appear as duplicates in less well maintained PGN files. Another trick is that some games are missing certain annotation fields. Some fields could also be filled in with incorrect type of data or simply be empty. So if you go down the road of writing your own scripts, consider writing quality check scripts that make sure the PGN format is followed and that the information is complete.
You can do it with ChessBase: http://chessbase-shop.com/en/products/chessbase12_download