Well it could be a 63 model that the factory converted to 64 style in
hopes they could get rid of the extra 63's. I know that fall of 63 when
Stude started production of 64 models in south bend, they still had
lots of 63's they hadn't sold to dealers yet. It could be that they
converted some to 64 type styling but had to leave 63 S/N since the S/N
was also stamped in the frame on some cars. It also could have been a
dealer left with too many 63 style cars and he retrofited the 64 parts
onto a 63.  Maybe the car was in a fender bender and the dealer just
updated the car for the customer. It was desparate times for Stude
during the Fall of 63.

Some states used to not issue titles until the vehicle was sold. I saw a
Cushman motor scooter that had a title 2 years after production ended.
It was simply in the dealers inventory for that time. It was well
documented as It came fron the original owner that had it for years and
records of registration. I also had a friend who worked for
International Harvester in the early 60's. Now this was a company store,
not a franchised dealer. They had vehicles not sold until well into the
next model year and they all got a year model of the year sold. In the
case of International, if a new model was sold before the end of the
year, that is what was on the title. Sooo there some that were actually,
for example, a 61 that could have a 60 title while another would have a
62 or later title depending on when it was sold.
I have seen quit a few vehicles from 50's & 60's where the vin didn't
match the year for the title and always suspected this is what happened.
Heck, I have a 1903 Oldsmobile replica, made in 1958 by Bliss that has
as 1902 Oldsmobile title. Now that is a different story but just shows
you can't always believe the title.