Pawn and Two: In the London 1883 tournament book, Mason provides the following information about the position after Winawer played 43...Nc5!:
<No doubt the reader will see what neither of the players saw at the time--to wit, that this is what is usually known as a "false" or "impossible" move. It was not discovered to be such until some days after the game had been played and when the official copy of the score came to be examined. It was a powerful stroke, and in every sense of the word a successful one, as it left White absolutely without resource.>
Based on his above remark, it seems that Mr. Mason had quite a sense of humor.
The editor of the tournament book, J.I. Minchin, then added the following note:
<The only explanation that can be afforded regarding this singular impossible move having been made and not detected is that the adjournment had taken place just previously, and the position of the pieces was probably taken down incorrectly on the diagram handed to the member of the Playing Committee, and Black's Knight was placed on d7 instead of e7, thus affording Mr. Winawer the opportunity for his brilliant coup, but for which the game would have probably been drawn.-Editor.>
Mr. Minchin is incorrect in stating that a draw would probably be the result, if the correct adjourned position had been played. As indicated in my previous post, Winawer still had a winning position after 43.Kg3.
Also, as noted by capanegra, the above game score is incomplete. However, it is not just the move 43...Nc5! that is missing, but also the moves 44 to 49.
Mason did not abandon the game after 43...Nc5; instead he played on until he was checkmated.
The final moves of the game were: 43...Nc5! 44.Qg2 Ne4+ 45.Kf3 Qe1 46.Qh2 Nd2 47.Kg2 Qf1+ 48.Kg3 Qf3+ 49.Kh4 Qg4x.