I don't know about Ludwig but I do have a Sonor Phonic series (1980s) concert tom with a bearing edge on the bottom*. Maybe some companies cut the bearing edges before drilling the lug holes and they use the same shells for both style drums.

*Curiously, I also have other Sonor Phonic concert toms that don't have a bearing edge on the bottom!

I don't have time to find the thread(s), but I have read, on here, that this was commonplace for drum manufacturers to put bearing edges on both ends. Usually they put a chrome strip on the non-headed side though. Guys with real-life experience can adjust this reply more closely to the actual facts.

Certainly Ludwig did with the 3-ply shells, and early on with the 6-ply. Basically, it didn't occur to them not to do it... shells had two edges, period! The result was, they were easy for drummers to convert them to conventional toms.

BTW, Ludwig's concert toms always had small lugs. So, when you see a '70s 9x13 or larger tom with small lugs, it's a safe bet that drum started out a concert tom. :)

Bermuda