The directive (#1032) to delete the diamond around the escutcheon and nut on NT and KT stocks was issued on December 28, 1967. However, it took over a year to deplete the supply of diamond targets. Generally, the last N-frame revolvers to be made with diamond targets shipped in very early in 1969 and have a serial number in the S300000 range. All 29-2s in the S315000 range or higher I have owned or seen shipped in 1969 with non-diamond target stocks if that helps.
Coke bottle stocks were phased out in place of diamond target stocks beginning in early 1966 and were completely replaced by mid-1966.
Below is a photo of S316488 shipped on August 19, 1969 with its original stocks.
Bill