[digismack]

If you change a software license, are users of that software bound to the new terms if they don't "update" to the version of the software released with the updated terms?

[schrijver]

No, you can’t apply licenses retroactively—if you have a version with the old license it is still under that license.

[vorg]

But you can stop supporting the older versions, say, by only applying fixed bugs to the newer versions.