You are right, there is a Registered logo above the G. However, they shells starting with 182xxxx are cleat coated, have re-enforcement rings with 3 ply shell. The one starting with 185xxxx also have re-enforcement ring with granitone paint.
From what I've read, from 1976, Ludwig switched to the Classic serie with no rings and 6 plys BUT in 1978 they made a "combo serie" with old 3 ply shells with granitone until they were used up. So my bet is that my drum are from that "combo serie" from 1978.
Ok, the drums sound great, but I was sold that they were from early 70s. I'm wondering if 1978 drums worth less than 71 even if the construction is similar.