The catalog number is usually the most prominent number printed on the release - often on the spine, on the back cover and on the label, etc. The catalog number should be entered directly as it appears on a release - it shouldn't be altered for conformity with other catalog numbers listed on the Label page.
A catalog number is required for every label entered. Where no catalog number exists, there is a value of "none" in the catalog number field (note the lower case "n"). For other companies on the release, the catalog number field is blank, unless there is a sequential identifying number that relates directly to the company.
This # is very important when identifying the quality and rarity of your Vinyl Record.
For more information on identifying a vinyl record click here: Catalog Number Guidelines