CHIME, CHIME, DING, DING.
I've been compiling a list of 12", 13", 14", and 15" 3-ply, 6-ply and vistalite B/O Badge Ludwig toms and there tone control placement.
Here is what I've found so far in a nut shell.
The lowest serial # I have found so far on a B/O Badge tom with the TC NOT OVER the Badge is 761575. The highest is 1257642.
Now Here's where it gets interesting.
The lowest serial # I have found so far on a B/O Badge tom with the TC OVER the badge is 11926XX and the highest is somewhere into 220XXXX area.
As you can see there's a bit of an overlap in serial #'s. And it doesn't end there. I have serial #'s of toms in the 121XXXX, 123XXXX, 124XXXX area with TC's OVER and NOT OVER the Badge.
As far as what year Ludwig did this I could only guess. Looking at the serial #'s I'd say maybe around late 1974 early 1975 to sometime in the mid 1980's when they discontinued tone controls in there drums. Again this is my guess and not fact.