Zuma, I like these discussions as well.
Just to be clear, I don't think the drilled bannerstones were atlatl weights. I think you don't believe that either, but I'm not sure. I get confused when you mention that a drilled bannerstone might be able to be slipped onto the atlatl from the narrow end. I don't believe this was done in the Southwest ( or anywhere else ) and I think you agree with this but, again, I'm not sure.
On a side note, as far as grooved stones go, I consider some of these to be atlatl weights but I have seen discussions that call these "bannerstones" as well and it can get confusing. There are certainly grooved stones found everywhere in the US and, since these are sometimes called bannerstones ( or boatstones ) , it's difficult to have a clear discussion sometimes.
I try to keep them separated in my side of the discussion by using only the term "atlatl weights" for weights actually attached to an atlatl and "bannerstones" or "boatstones" as mysterious items.
Your experiments with bannerstones as drill weights is very interesting. I think you are definitely onto something. I think drilling was important enough to spend time making "fancy" tools for drilling. Drilling is certainly a more logical use for the bannerstones than for atlatl weights, simply because atlatls are subject to a lot of abuse and are easily dropped or otherwise mishandled which could lead to the breakage of delicate bannerstones.
Again, just to be clear, there are real atlatl artifacts that clearly have stone weights attached. I believe that atlatl weights were used and that there is no doubt of their existence.
Some have put forth the idea that drilled bannerstones would slide up and down the atlatl during a throw, but I don't see any logic to this idea whatsoever.
I'll try to find some atlatl artifact pictures from areas other than the southwest. I think I remember seeing some from the Northeast.