the single version is slightly different than the more common lp version. on the single there are additional backing vocals but it's still the Andantes. If you listen to the 50th anniversary cd set of the girls, you have the single version

I'm not sure of the differences with the Japanese GH.

Mary and Cindy are singing on the pre-recorded track for the Sullivan appearance and are then lip syncing on the show. Supposedly because the background vocals are hard to make out on the 45, M and C just skipped the lyrics and did the ahhh's. Often the andantes would create the lyrics, harmonies and lines in the studios while recording. therefore the backing vocals and lyrics might not have been written down on paper to sing from.