The slash at the end of CC licenses is not added, see e.g. edit #17810977.
This is not as easily solvable as I thought, because adding a slash at the end is only possible if we know when a license is at the end. So this would be either a very long regexp, or we need a list of all (valid) CC licenses.
E.g. a naive approach would be:
url = url.replace(/^(http:\/\/creativecommons\.org\/licenses\/.*[^\/])/, "$1/");
but it would add a slash immediately after "http://creativecommons.org/licenses/b".
For the solution of MBS-3956 (protect license URLs) we probably need a list of "protected" URLs anyway, so maybe we can introduce it somehow (maybe in the code, maybe in the database)?
In review at http://codereview.musicbrainz.org/r/1949/