Thread:Project:Support desk/Extension version numbers not displaying/reply

Since MediaWiki 1.25, it depends from where the information is taken:

"version":"1.25",
 * If the skin has a skin.json file or if the extension has a extension.json file, then the version information is taken from the key "version" from inside that file. Meaning: You can add it there, e.g. below the line with the "author" information and it will display:
 * If no skin.json/extension.json file is present, then the version information is taken from the array $wgExtensionCredits in the central skin file/extension file.

SpamBlacklist and the skins do have such a skin.son/extension.json file.

For the skins coming with MediaWiki 1.25 I can confirm that you have that problem, because the "version" information is just missing. You might want to report that to Phabricator so that it can be added.