This part.
It's a little odd.
What's odd about it? With the exception of writers who have book that flop miserably, there is no reason to write the next book before getting a contract. Only the first third of the contract money is at risk, and track record takes this risk away.
You do have to tell them what the next book is going to be, and they have to agree, but why would any sane publisher make you wait until the book is finished, or the book way well go to a different publisher. That would be horrible business procedure.
And why would most second contracts out there have the "upon delivery of an acceptable manuscript" if the book were already written? It's also why second contracts have a delivery deadline.
It's no different at all than a two book deal, or a three book deal, or a ten book deal. You've only written one book, but the publisher gives you a contract for additional books. This can happen two books at a time, or, as with James Patterson, seventeen books at a time, or a single book at a time.
Big number contracts, such as Patterson's, ensure the writer is tied to that publisher essentially forever. Small number, two or three book deals, ensure the writer is tied to that publisher for two or three years. Single book contracts ensure the writer's next book goes to that publisher.
Money is usually paid out as the books are written, not all at once.
An outline, a synopsis, partial, etc., is nothing more than an excuse the publisher uses to give a writer a contract, and guarantees the writer's next book goes to that publisher.
I didn't even have to wait long before this started happening. After my first novel sold, I started working on the second. When my editor and I talked about the fist novel, and I told her I was busy writing the second, she was surprised, and said, "You know you don't have to actually write the second novel before we give you a contract? Just send me a synopsis of the book."
It's been this way ever since.
It's just not smart to allow a writer who's making you money finish a book that may sell to a higher bidder. The contract you have in hand should state that the publisher gets first crack at the next book, but the sale is never automatic unless that particular book is under contract. You're always free to look for someone who will pay more. A contract before the book is written means you must let the publisher have the book, if they like it.