I misread all the serial number discussion too. Sorry. The 7 digit serials make sense in terms of the year, and the year makes sense of the rest.

There are 4 mounting holes (now nicely filled with bolts by the look of the photo) which indicate that the bass drum originally had the center located rail mount as Jazzettes did. But it was replaced by a non Ludwig mount system. That's a nice mounting system (Slingerland Set-o-matic? I'm not sure from the pic) but since it is not original it probably lowers the value a little in the eyes of collectors.