Factory build sheet discrepancy

What are the first six VIN digits?

Does the VIN on the build sheet match the tag in the door pillar?

I've seen very very few factory numbers mistakes.

All but one have either been a missing digit, or two digits transposed.

I'm not sure about engine swaps after the purchase of a brand new car being "common" back in the day. Perhaps in professional drag racing circles.

What is quite common however, is for a back seat containing the build sheet for a different car, but having the same interior, to be installed in any given car.