In 1965 NEC, there is no mention of bath receptacle (210.22 (b)) But, it shows up in '75 in 210.24 (b).
Ah... So not there in '65, but the requirement is listed under 210.22(b) in my '71 NEC, so I guess that narrows it down to either 1968 or 1971.
In fact looking back at the '71 code I've just noticed that there's the vertical bar against the two lines which say "At least one wall receptacle shall be installed in the bathroom adjacent to the basin location."
Unless the wording was different in 1968 (which doesn't seem likely for something so simple), I guess that probably means that this was a new requirement in 1971.