Earlier quoted context omitted.
> In the case of the author licensing his work, he may license it in any way he wants, to as many entities as he wants and the licenses don't care and cannot disallow this. Actually, its quite possible for licenses (though probably not gratuitous licenses) to disallow this; a license can, for instance, by its terms be either completely exclusive or include some exclusionary provisions. In fact, such licenses are very…
If only the owner of the copyright can claim infringement (as is the case in the US), then the point is moot. Is J. Doe going to sue herself for violating a license by releasing under another license?
An exclusive license is a transfer of those rights under copyright to which it is exclusive from the licensor to the licensee. So the licensee would be, for the rights in question, the copyright holder, even if they were not the creator and the holder of the remainder of rights under copyright (see 17 USC Sec. 101, 201).