Here's a real rough example of how the VON is assigned for non-special order (i.e special paint), package (A12s, Daytonas, Superbirds, etc ) or other specialty VON (Police, taxi, dealer demo, etc) cars for 1968 and later.
January 5th- Sales manager forwards all order sheets to the regional office. Sheets are sent to Headquarters and routed to plant. These two order sheets wind up at the Hamtramck plant. Orders are sorted internally and scheduled for production. At this point, the only unique identifier to each car for billing and scheduling the car is the VON. The VIN has not been assigned yet.
One would expect to find consecutive VONs from the same dealership because the order pads would be numbered sequentially. As pads were disseminated from a regional office in somewhat of a large series, one should also expect to find similar VONs from a certain region.
Hope this makes sense.