The Beatles bounced tracks between two 4-track machines a lot
say tracks 1,2,3,4 were full on one Studer j-37 4-track.
They then would merge say tracks 1 & 2 together on the 2nd 4-track
leaving tracks 3 & 4 alone on the 2nd Studer -37 4-TRACK
2nd 4-track
track 1. 1&2
track 2. empty...