chasing numbers

My 70 Super Bee has the vin number 178431 on the block, tranny, radiator support. I was looking at the trunk rail and it has the number 74178 which is only five numbers compare to the six number of the vin. Th last three numbers are consistent with the first three numbers of the vin. The 74 has got me confused. I don't think the quarter was ever changed but I could be wrong. Anyone have any ideas. Thanks

I'd probably climb in the trunk with a flashlight and check out the underside of that quarter/drain rail

Mistakes are possible? If there is absolutely no sign of it being changed I would assume that it is infact a mistake from the factory. Usually they're are just a couple of digits inverted or something, but who knows. May have been the first car after a long lunch or a new guy on the job?
KID