Rick Gier (kcdrumdad) distinguishes between the blank B/O badge and the trimmed B/O badge. The blank version has the space for the serial number but no number in residence. The trimmed version has that area trimmed off. The trimmed badges are found on metal shelled drums with a center bead where the full badge wouldn't fit because the hole was drilled for the Keystone badge position not the B/O badge position.
Which badge have you got on your Supra? Full or trimmed badge? And have you got a date stamp?
Maybe they just got a few boxes of badges without serial numbers on them.....Serial numbers were put on badges in late 1963 because of a law passed in congress. Maybe the law expired, or quit being enforced?
I heard serial numbers were included because the insurance companies pressured them to do so, but that claim lacks proper references. Have you got a reference to Congressional legislation by any chance? If there were such legislation one might expect that it wasn't specifically about Ludwig drums and would have applied quite generally to manufactured goods.
In Rob Cook, The Ludwig Book, published by Rebeats, 2003 page 210, Rob quotes Chuck Hueck on procedures at Ludwig:
When we received the badges from the manufacturer they were wrapped in cellophane and in numerical sequence. They got unwrapped and tossed in a box by the drill press where they got mixed up. That's why it was probably fairly unusual for a drum outfit to have sequential serial numbers.
so yes maybe they just got a cellophane wrapped set of badges without serial numbers some time in early 1970. Once the blank badges were tossed into the bin by the drill press they started to appear on drums.
According to Rick Gier he had recorded 2 blank Keystone, 3 trimmed B/O from 1969; 3 blank Keystone, 43 blank B/O, and 8 trimmed B/O from 1970; and 2 trimmed B/O badges from 1971. That was at time of publication and he's had more data since his work came out:
Gier, Richard, Serial Number Based Dating Guides for Vintage Ludwig Drums. Published by Rebeats, 2013. Page 19.
So 1970 is the most common year for B/O badges without serial numbers. I've got a trimmed badge Supra with a date stamp of Dec 19, 1969 which I picked up after Rick's publication came out so I believe mine would be additional to his data.
Rick will have a better handle on the data, but from what I know most drums from 1970 do have serial numbers. Only a small proportion have blank or trimmed badges. That makes the "only serial numbers for schools" scenario unlikely, unless almost all the production from 1970 was destined for schools and Ludwig knew this at the time they were attaching badges during the assembly process. Does it really make sense that they would have switched to having two separate piles of badges just to make such a distinction? Treating badges for school orders as special and different certainly doesn't fit with Chuck Hueck's description
I never recall Ludwig ever recording serial numbers. We were so busy that we would have had to hire a couple more people just to do that!
and he was working there from 1972. Maybe things changed dramatically between 1970 and 1972 in terms of production processes, but I'd presume things stayed the same in the absence of good evidence for change.
Hope this helps.