Hi Fat Lady,
That is the game I was trying to recall to post. I remember seeing it
shortly after it was played. I think you sent it to me.
Swiss G with his Knight on e6 preventing castling reminded me of
A game a Sandy Bells player had in Div 4 in the 90's.
He too had a Knight on e6.
(the lad is actually active on RHP, he's shy and never posts so I won't name him.)
This is not the position but the incident and the idea is right.
Black played 0-0-0.
White (the Bell's player) instead of playing Qxc7 checkmate and thus
ending the game pointed out the error.
The Black King uncastled another move was played. White eventually went on to win.