Post some pics.
Usually they are option codes, or a heads up for downstream workers on paint colors and such.
http://67-72chevytrucks.com/vboard/s...light=sequence
http://67-72chevytrucks.com/vboard/s...light=graffiti
http://67-72chevytrucks.com/vboard/s...light=graffiti
http://67-72chevytrucks.com/vboard/s...light=graffiti
http://67-72chevytrucks.com/vboard/s...light=graffiti
They will not match the VIN. Nobody in the vehicle assembly plant cares about the VIN - everything is keyed off the build sequence (or manifest sequence) number. The build sequence number is an attempt to control the flow of subassemblies into the main line, and keep everything in order.
The VIN is just a part to be installed on that particular build, just like a tune up label, SPID label or Mulroney window sticker.
K