My guess would be probably not because most of the time, declining will lead to the 2...d5 Alapin or 2...Nf6 Alapin by transposition.
They might cover the real obscure ones that fo not transpose, but you will likely need a book on the Alapin if you are going to play the dubious Smith-Moron Gambit
Does Mark Esserman’s book, Mayhem in the Morra cover Declined Variations? Sadly, not every player Accepts the gambit.