A licence like a Creative Commons cc-by-sa is not exclusive, and allows the copyright holder to do what they like with their work. What they can't do is revoke

A licence like a Creative Commons cc-by-sa is not exclusive, and allows the copyright holder to do what they like with their work. What they can't do is revoke the licence terms from anyone who chooses to exercise them. At best, the copyright holder can request removal of attribution. In another comment I mention the Geograph project which uses cc-by-sa. For some more background to that, I wrote about the reasons for selecting that licence to ensure long-term freedom of the archive here: http://www.geograph.org.uk/help/freedom http://www.geograph.org.uk/help/freedom