The bead of the Selmer is not an added piece, just the edge of the bell rolled back and formed into shape. Selmer were not the only ones to have this bead, my Buffet-Crampon has a similar one.
I have not looked at one in person. I would like to see if there are clues as to how it was done.
That would be quite a task to accomplish since the metal folded back would have been stretched out wider on the mandrel and would have to be compressed back to a smaller ring in the process - which is why inserting a ring of flat stock and pinning it with the rolled edge bead is the more typical approach for both free-standing garlands and applied garland-like trim.