My late wife and I were once invited to contribute to a recording that a very nice-sounding musician was doing, and he kindly let us have a copy of his guide-track (with guitar and vox both played by him at the same time) to learn from.

Because he was so used to playing the song without others, it was indeed in the time signature of "one".

Eventually we invited him round to out home and played the guide track and invited him to accompany himself as if doing a second guitar track overdub. He couldn't do it. He then conceded that the track should be started again and we rehearsed it together so that the timing became repeatable.