Shamelessly swiped from another forum:





I'm not 100% sure what "Job 1 date" means but I'm guessing it is the date the first car either starts on the production line or leaves the production line.

 

Job 1 is the first day of consumer level production; starts on the line. Everything prior to that is pre-production or prototype vehicles not intended for public sale at a dealership level.

My company uses these internal designations as well.