Problem arises when a guy needs to buy a brake caliper spring for a 98 WRX that has 4 pots fitted to it for example. He can quote his VIN 'till the cows come home, he'll never get the right spring. Some interpreters can listen long enough to get the story and work out what you need, others can't.

I just keep a list of VIN's that I know have certain parts. If I need a part for a RS Liberty with Brembo brakes and a 6 speed transmission I use an appropriate VIN when ordering.