I've been trying to figure that out, and as far as I've found, Lay Me Down features Rome, the Dirty Heads are separate outside of that one song featuring Rome, but did it before he got picked up by the old guys.
Sublime is doing it too late. Like they realized what they missed out on. They don't even seem to really want to do the tour, they just need to. After finally settling on $$, name usage, copyrights, etc, they just don't seem into it.
The Dirty Heads are really good.
This may answer some questions, 1:20ish explanation