Some of them are in like Hoppe, Cochran, Layton, Worst and De Oro. I've always wondered why Kieckhefer, Reiselt and maybe Horgan weren't talked about more as candidates.This is the list of the World Three-cushion Championship which was held in the U.S from 1878 to 1961. I can't help but think some of these players are worthy of the BCA Hall of Fame.
List of world three-cushion billiards champions - Wikipedia
en.wikipedia.org
There is a limited amount of interest in the "overlooked veterans" section of the BCA Hall of Fame. There are many more recent veterans that are much more likely to be included than the ones you have mentioned. I'm betting that Horgan is known to fewer than two of the HOF voters.
Ceulemans was a UMB World Three-cushion champion, the two events since 1928 ran alongside since each other as "World Championship" events, Alfredo De Oro although a Hall of Famer, is often overlooked in the history books.
The UMB has been the sanctioning body for the World (Professional) Three Cushion Championship for some time. I think the operative distinction is between pro and amateur. Again, I think the title you have chosen for your Wikipedia page is confusing.
I think it's also useful to note that the sanctioning body for the American championships was Brunswick (BBC Co).
Side question... Who ran the old interstate league, which is where Kieckhefer and Reiselt mainly made their names it seems was that Brunswick as well?