I looked into it a bit more and I was a bit wrong. It gets interesting.
The SOUL CITY release is definitely from 1974, but it seems to have been a cash-in release to capitalize on the success of "Rock Your Baby". The SOUL CITY 45 carries a United Artists catalogue number (XW-456) which places it as a 1974 release (the previous UA distributed 45 with cat# XW-455 is a Blue Note label release by the way). I don't know when Soul City ceased to release records on a regular basis, but the label seems to have been reactivated for the George McCrae release.
Here is the mention of the Soul City 45 in Billboard Magazine from 20 July 1974:
In the same issue, the "Rock Your Baby" LP is reviewed as well which seems to back the theory that the SOUL CITY 45 was a cash-in attempt:
However... the UNITED ARTISTS issued US 45, with cat# 50811 seems to have been released in July 1971! It is mentioned in Billboard Magazine from 31 July 1971:
Now I'm actually not 100% sure where the BLUE CANDLE 45 fits into it all, but I still believe that it was the local release prior to the UA 45. It can't be from 1974, that would mess up the entire Blue Candle discography.
The european UNITED ARTISTS releases that I have seen of this 45 are however from 1974, mirroring the SOUL CITY release.