When I first started buying records, I noticed that they often had hand-etched letters and numbers in the blank space between the last song and the label. At the time, not knowing anything about how records are made, I figured they were etched by hand onto each record by the company and denoted a numbered order of production, like a limited edition artist print. That would be a lot of writing! I chalked it up as another reason why new vinyl is so expensive.
When I discovered I could use Discogs.com to catalogue our records, I searched for some kind of identifying mark on the record itself and found that the etched alphanumeric string is called a matrix or run-out code. They do not count “up” with each new record produced.
The first part of the number generally matches up with the catalogue number of the record and will also be on the label. The other information records the A/B side, the “cut” of the record stamper, and often the pressing plant or the mastering studio / engineer. Most have numbers or letters and dashes, but I even have one with a tiny flower, one that says “Porky”, and Paola has a green vinyl with a miniature signature!