Rats, the ad is pulled before I even got to look at it.
It's usually the other way around, the '64 hearse could have '63 tail lights and bumpers on it. They started with a '63 commercial chassis and body made sometime in '63, then sent it to the private coach builders (Superior or Miller Meteor) where they make it a hearse. That could take 6 months or so depending on how many orders they have, so by the time they are finished, it is already 1964, so they just call it a '64 hearse since it is technically brand new and finished in '64.
I have seen '63's with '62 ass ends. but never the other way around. Maybe couldn't tool up fast enough for the new year. But commercials like you said took a long time to build. But seeing a commercial with the previous years ass and roof is not all that uncommon. Like seeing a commercial is all that common any way. With a production run of 2 to 3 thousand units per year. Including combo's and ambulances for all coach builders.