Don't know what to say Aisling except I'm guessing my book is wrong then in not mentioning your stateroom as well as Piper's. The book was published in '98, by what appears to be Disney itself. If you are a party of 4, I would say they would have to give you a room for 4 ---nothing else would make sense.
I suppose, let my list be a general guide to where the "sleep 4" rooms are and now I know it's not as accurate as it could be.