Not all barcodes are alike. If you're not sure whether you have a Codabar, Code 39 or something else, check out these links. It may affect how you enter your data into the registry.
Here is a sampling of vendors who sell barcodes. These are offered for information only and does not imply an endorsement from the Alaska State Library.
To find whether a particular identifier is being used, open the PDF file, then hit control-f, and search for the identifier you want to use.
If you don't find your proposed identifier, you're good to go. Otherwise, please consult your system administrator.