I think Michael is right.

To the best of my knowledge, publishing rights are basically the sheet music rights. If anyone wants to print the lyrics to Don't Dream It's Over, or I Got You, they'll have have to pay a fee to Universal Music Publishing. The owner of the publishing rights also gets a royalty when someone plays a Crowded House or Finn Brothers or Neil Finn-penned Split Enz song on a jukebox or the radio or does a cover version of one of his tunes.

But there are things the publisher can't do. If EMI remain owners of the actual masters, I suspect they retain first dibs on releasing what's in the vault, and Neil would have to enter into complex negotiations with them over a box set of odds and ends.