Albums
Album matrix numbers are often similar to the catalogue number. For example, a record numbered X-1234 may have a matrix number like A–1234 or X–1234–A on side one, and B–1234 or X–1234–B on side two, as shown on the label. In the run-out area, the latter number could be expressed as X–1234–B7, where 7 is the cut number. In other instances, the matrix numbers may be a separate series of two consecutive numbers such as 55667 and 55668.
Read more about this topic: Matrix Numbers