Four new results on the uniqueness of optimal superimposed codes are presented, namely, the uniqueness of (w, r) superimposed codes of size N x T with N = (w + r + 1 w) and T = w + r + 1 and the uniqueness of (2, 2) superimposed codes of size 18 x 9, (2, 2) superimposed codes of size 14 x 7, and (3,3) superimposed codes of size 66 x 11.