On Wednesday, April 11, 2012 at 12:45 PM, Sarah wrote:

Can anyone point me to the basis of the claim that cc licences are
irrevocable?

On Wednesday, April 11, 2012 at 12:45 PM, Sarah wrote:

 If someone were to upload an image to Flickr with a cc
non-commercial licence, then changed her mind and broadened it to
allow commercial use, Commons would not reject the image on the
grounds that the first, more restrictive, licence was irrevocable.
Not exactly. The license is irrevocable =/= license is exclusive. We don't *have* to follow the NC license. 

Say the work was once BY-SA-NC and later changed to BY-SA, people can still create derivative work and license them with BY-SA-NC, *not* BY-SA.

(Do correct me if I'm wrong)

Best regards,
Benjamin Chen / User:Bencmq