The nodeos software provides a version number based on the git commit. Depending on local patches, the same version may generate different version numbers. The list of version numbers is maintained by hand in GitHub. The list also specifies which versions are considered current vs out-of-date. Generally the last 2 to 3 versions are considered current, although if a long time passes with out a new version being issued or there is a critical issue, then only latest version is considered current.
If your version is missing, please generate a pull request or request it be added by contacting email@example.com or @mdarwin on telegram and keybase.