Singles
Records with one song per side, particularly 7-inch 45 rpm and 10-inch or 12-inch 78 rpm records, are often found with non-consecutive matrix numbers on each side, and the "hit" side or "side one" may not necessarily be the lower number. This indicates that the numbers were probably assigned at the time the songs were recorded. If there is a significant gap between the two numbers, the songs were probably not recorded at the same session. If the numbers appear to be from completely different sequences, or have a different format or number of digits, this can indicate that the numbers were assigned by the recording studio, and the two sides were recorded at different studios. When record historian Brian Rust researched his discography books on early recordings, he was able to determine the studio and approximate recording date of certain songs from matrix numbers by comparing them to other numbers in the sequence.
Read more about this topic: Matrix Numbers