There's probably more than one reason. 1) People were generally less than thrilled about the change from silver to cupro-nickel - it was only imminent decimalisation that changed that. 2) The first decade of Liz II is often poorly struck, with shallow designs that wore quickly 3) By the time that people were pulling stuff from change (late 60s), those earlier coins had already had a good deal of circulation The big question is : why are some 50s dates so much harder than others? My own theory is that some years were minted but not fully issued, so Mint bags got distributed to banks significantly after the date on the coins. You also spoke of the 1958 and 1959 halfcrowns - it's worth pointing out that the 1960 is criminally underrated; in fact, only 1966 and 1967 are common in genuine BU.