I was figuring the O (overload) stood for the c4 pawn screening the c1 rook from the c8 rook and defending d5. What is wrong with 21. … Nd5? (hits the f4Q and the e3B and taking it drops the c1R).
I came up with the Overload idea to describe tactics that work by attacking a target with too much force for the defense to prevent. The 1st target is the White Bishop. Nbd5 adds another attacker (with the Black Queen) to the Bishop which is only defended by the White Queen. However, the c4 Pawn can remove the Knight attacker, ending the Overload.
The problem with cxd5 is that the Pawn was serving a purpose by blocking the 2nd target (and actual one) the White Rook. This is an Overload by the Black Queen and Black Rook attacking a piece that is only defended by one piece, winning an exchange (since you gave up the Knight to start with).
So, I would call the “c4 Pawn screening the c1 rook” a Pin (the P in DROP method) and not an Overload.
I can understand why the move was missed by both players. It is not a one move tactic. It is a tactical combination that includes a Removal (sacrifice of the Knight), multiple Overloads, and a Pin (sort of).
If only it had a Discovery, it would have spelled the entire DROP method!
