Martin:

Both boxes are Imperial Metal Industries Ltd., which means they were loaded after Imperial Chemical Industries' Metals Division was partitioned off and separately incorporated in 1962. IMI remained a subsidiary of ICI until 1978.

22 N O = 22 July, 1966

4 K L = 4 April, 1963

The /S is not part of the date code. It was used to indicate that the cartridges in the box were steel jacketed. This usually means that the contents were solids, but not always, as steel-jacketed soft points were offered in some calibers.