The same goes for Missouri. Licenses are through the Missouri Department of Revenue. The Director of Revenue in Missouri has some of the same duties as the Secretary of the U.S. Treasury. IMHO the DL # is the State equivalent of a tax ID number.
Re: Notice of Sale
Regarding notice of sale, again, without the notice of sale, the DMV/DoR will hang on to the last known registered owner information. They need notice that the previous owner is no longer owner(surety) on the automobile so that they can de-register. They are aware that automobiles are exported to or purchased in jurisdictions where the buyer doesn't have to register. For example, someone can purchase a 2015 pickup truck and use exclusively on a private racetrack or a farm--no plates needed. The notice of sale to the previous State of registration notifies them of the change. Having the previous owner sign it and include their DL # is a good idea IMHO. It might not hurt to send a copy of the bill of sale or bill of assignment as an enclosure.
The notice of sale signed by the new owner and the former owner should serve to prevent them from going back the last known owner.