Oklahoma does NOT recognize a bill of sale at all. It is a useless piece of paper, in nearly all cases. They require a title on an Oklahoma vehicle or on a vehicle that comes from a title state. Also, if a vehicle is brought in from a no-title state (Alabama, Georgia, New York, etc), then there HAS to be proof that the car was/is registered in that state in the seller's name. And believe it, not every DMV employee is a complete idiot, at least, not here. They know exactly what states require what, and require that documentation to gain an OK title.
Hell, I brought over a '67 Belvedere I wagon in 1992, that was sold new in Belgium. I registered it while in Germany through USAEUR (US Army Europe, for those that do not know). Shipped it home through Houston and drove it to OKC. In Oklahoma, I had to show the original Belgian paperwork, the bill of sale translated (which I was able to to, and remember, no title on this one, as it was sold new in Antwerp, Belgium in late 1967!), and the USAEUR registration, and got my OK title and registration. The title clerk at the state Tax Commission (our DMV) knew what docs to ask for and what the process was. I was pretty impressed, actually! This whole deal took maybe 30 minutes.