Yeah, and also, it's been attributed to the delivery of cement in a cement mixer, with the claim that a full cement mixer hold nine cubic yards of cement, and thus, emptying it means unloading the whole nine....etc.

Truthfully, there are tons of these books out there, and as with anything - history, folk music - to be sure, there has to be documentation. And that particular phrase is fascinating because of the dozens of origins attributed to it.