VN=Van Nuys also known as LOS for the Los ASngels Planty. they chnaged the Cowl tag to VN druing the 69 production run. The VIN plate kept the L for Los Angeles. These cars did not get an "X" code on any of their cowl tags.
NOR= Norwood Ohio assembly plant and starting in Dec of 68 I beleive they started using the "X" codes.
This being said , its one of the major reasons to get all Doc's when you are buying what is said to be a Big Block SS Camaro from the Van Nuys plant.
Kurt S and the folks at the Camaro Reseearch Group Have some outstanind facts withing their web site.
http://www.camaros.org/numbers.shtml#CowlTag
Also go to their main page for the site plenty more to keep you busy reading