It's very possible that both trucks were registered as 1967 trucks because they were 1968 trucks SOLD before 31 December 1967. Remember, many states registered NEW vehicles as the year they were first SOLD, versus the actual model year. This was not an uncommon thing, up through the 1968 model year. After that, the registration scheme nationwide was standardized so that the MODEL year was used, rather than the year of first sale.