Board Thread:Support Requests - Getting Technical/@comment-26967806-20150908153233/@comment-26009167-20150908164633

Dessamator wrote: Well, there is an issue with that. Even if they change it to non-commercial, everything uploaded up to the date before  they make such a change will have to use a CC-By-SA license. So someone can for example copy and sell the content  created before the change was made.

Also CC license is irrevocable:

I feel this is worded wrong. How I understand it is this:
 * See https://wiki.creativecommons.org/wiki/Frequently_Asked_Questions#When_do_Creative_Commons_licenses_expire.3F

The contributions made by the users can have their license changed at any time, and perhaps relicensed to Wikia in that form (or at the very least, Wikia continues to be able to use them under the old license - I'm not 100% sure on this point but either way Wikia is still legally allowed to show the content to other users). Any usages of the content before the change will stay under the original license, but any new usages (whether derivative of the old usages or not) will be under the new license unless the original author says otherwise.

Remember that Wikia is not the one licensing the content given to it out to everyone else - they never have and never will as that in itself is another right that the author must give them. Rather, they just have the license to show it and to put ads on it (like they do), which is implicitly agreed upon when the user submits those changes.

Please correct me if I am wrong, but that's how I understand the copyright system.