The 1966 is NOT a release date, but the song published date - sometimes its the year copyright is claimed. The release date is always when the record company formally list it as 'availilable' and actively promote it. (Come to think of it, some often fail to promote anything well enough ! )
This one was from the days when Liberty was inside EMI - they later set up shop themselves in Mortimer Street,W1, when they became part of United Artists.
A corking version, P.J. In '72 Bobbie Gentry and Bobby Darin sang a medly of 'Niki Hoeky' 'Polk Salad Annie' & 'Never Ending Song of Love' on Bobby's TV show. It's just been released on CD and jolly fine it is.