The shell on that drum is the same shell used on the b&b drums that were issued just before. What we are seeing is a seam that was done a little differently, in the normal course of a production environment. Maybe for a day or a week, the seams were done that way by whoever was brazing the shells together at the metal shop where they were being made for Rogers.
It is not a 'prototype' or anything like that: the prototypes of this shell were made long before the beavertail lugs came along.
What we have here is the usual seller hyperbole (b.s. to those of you in Yorba Linda) because he hasn''t seen one like this before. If he knew the Rogers shell/lug/etc timeline he would know that these shells had been around for a while before his drum was built.
And the serial tags were pulled from a box on the bench, where they were all mixed up from being handled. This drum and the one mentioned above were probably built in the same 1-2 week period....