Here’s an abbreviated version of a very nuanced topic....
VONs are the first and basic unit used to sort cars and help assign VINS so depending on the situation VONs may or may not be sequential to VINs.
If a company or government agency orders a batch of similar fleet cars, say “cop cars”, the VONs and VINS will likely be sequential as the cars would be built at the same plant at the same time so the can arrive as one shipment.
Promo cars are often sequential VONs and VINs.
Package cars were built at a designated plant. You may see VONs in clusters but you may or may not have sequential VONs and VINs for daily production.
Cars built at multiple plants ( say Belvederes or Coronet based cars) may or may not have sequential VONS for things like special paint.
Cars built for non timely situations or based on administrative things like leases or true special order cars will probably not be sequential.