Hello,
Having a groove there does helps to increase contact pressure, so long as there is a o-ring. Brad's regulator end isn't like that when used. There's another piece of white ring that fits around the brass protrusion.
As far as whether it is for CO2 use. I have no doubt in my mind it is. These regulators are for bar use with much much higher CO2 flow rates, than the typical welding or aquarium use that we see elsewhere. As such, there is no misfits or anything here that I'm sure. As the rest of the regulators I have in stock are all like that.
Brad, let's wait and see what Micro Matic say. If you ended up coming to Vancouver to visit J&L for a new regulator, let me know. I'll see if I can put another one of mine on your CO2 bottle to see what really is going on. If not, I'll give you a refund, since you are so nice.
Titus