i was also thinking if you work at a place awhile, wouldn't you make a "cheat sheet" that helped you look up parts? such as VINs to use just to look up parts, keeping in mind some of the major mid-model year changeovers?
i could definitely see not actually ordering any parts without the VIN, or having a policy that without VIN the customer would pay 25% restocking or some large fee if they didn't want a part ordered without VIN.
i can see plenty of unreasonable customers getting ticked at both sides of this issue:
What, you can't order a part without the VIN???
OR
Hey, this is the wrong part why can't you idiots get me what I need (after an order without VIN)???