I think Tenderloin is going to have to answer this. In Lazlo's "Donaldson's Series", he made mention of a fourth book in the series named "Submarine Dreams". Was it ever written or is it only in the dreams of his fans? When I really need to laugh, I reread the Donaldson's. A fourth book would be amazing.
Lazlo died of lung cancer, in 2018 IIRC. I doubt there are any finished but unreleased works in the queue.
Also he's a great author and not yet behind the paywall so forum readers new to SOL should give him a try. I recommend Emend by Eclipse. Two failure misfits get to start over as young teens and edit their lives through hard work. They don't have super powers or knowledge of hidden stacks of cash, so their changes are local but important for those they affect. The combination of many small edits by many people create a butterfly affect that changes the world.