Quick timeline:
2000-2003In some of the MP3 series of cases, judge Rakoff held that, given the law as it is, retroactive licenses from a co-owner of the copyright are fine, and they extinguish claims of infringement from another co-owner.
Copyright.Net v. MP3.com, and
Country Road Music v. MP3. Com.
For example,
the unambiguous language of this release creates a retroactive reproduction license that cures any past infringement by MP3.com of these works.
It seems clear he accepted it, as that was the law - there were some precedent cases already.
2007The Davis v. Blige case in the Second Circuit held that between co-owners, no there can't be a retroactive license or transfer done after an infringement occurs. The court didn't decide only that, though; it also stated its conclusions in broad language, which sounds like it applies to all situations, sole ownership and co-ownership, not only co-ownership.
Such as,
Licenses and assignments [...] are prospective.
2016In the Palmer/Kane v Rosen case, judge Rakoff takes this language to mean what it says: that there are no retroactive licenses as a matter of law in the Second. In sole ownership situations, as well as any.
what Davis described as its holding — "that a license or assignment in copyright can only act prospectively" —
[...] is unambiguous and the result of full judicial consideration.