Cool pic! The black body yours was modeled after seems more radical at the bridge end. The PG and bottom horn in the Sunn ad look slightly different. The bridge and knob locations relative to the body outline are different on all three. They're all one offs! I chose the Fiesta Red one due to personal preference and this pic in Bass Culture. You can see the matching reflections on both the guard and body rings. Whatever, we love 'em all. Long Live Rock!
My wacko theories for missing rings:
Some of the donor 'Birds were NRs so they only had one ring.
Adjusting the truss rod involves removing 15 screws since there's no cut for adjustment in the guard. Maybe JAE's tech got tired of that. His action was so low that adjusting the neck was done quite often, strings got changed and setup checked for every show.