A release number, also known as matrix number or catalog number, is an identification number for your CD. It is used by record stores and online retailers as an inventory number. The factory also uses it to track the various pieces of your project through the production process.
The number usually consists of a combination of up to seven letters and numbers (such as CD1001), which can be picked by you and based on any combination of letters or numbers – your band name, artist’s name, special dates or numbers, etc.
If your music is released in several formats (CD, vinyl, etc.), you would use the same release number for each format, and append a configuration digit to your release number -2 for CDs, -1 for vinyl (example: XYZ346-2). This is the same code system used for the UPC barcode.
So if Crescent Music Services where to relese an album, we might use CMS as the first part of our release number, so CMS001 would be the full release number for our first release, CMS002 for our second release and CMS003 for the 3rd and so on. Or we might use CRES001 or CRMU. You get the idea.
Look at your cd collection and see what others have done.