So, referring to the multitude of copyright infringement lawsuits Trumpco is defending, one of the oldest is Eddy Grant's, for Trump's unlicensed use of Electric Avenue.
He's actually raising a defense, that probably isn't too common in these suits.
Grant alleges ownership of copyright in the music and lyrics, which is the subject of one registration, as well as a registration in the actual performance/recording of the song itself.
Apparently, though, the copyright in the performed version was registered as part of an album by Warner Brothers. That's actually normal, as the record company usually registers and initially owns that copyright, as they usually pay for the studio and producer. It is these rights, in addition to "master recordings" that artists usually buy back, or get back as part of the recording contract.
In this case, however, Grant had already independently recorded Electric Avenue and then licensed it to Warner, who released it as part of a greatest hits album and registered the copyright. All that is fine, but there is a question as to whether the album registration extends to the single preexisting song Electric Avenue. Normally, it would, because the record company initially owns the copyright in everything in the recording except music and lyrics, but this presents an oddball case.
I suppose that having one of the two registrations may halve the damage award to which Grant is entitled. So Trump is still gonna pay, or be ordered to pay, the question becomes how much.
I don't think this scenario will be common at all, but copyright stuff can be weird, especially the way they are registered by various parties in the music game.