When I was thinking about building a Rebel, I also noticed that. I emailed ram and got this response.
"We understand you are interested in the 12 inch radio! The package does include the 19-Speaker Harman Kardon® Premium Sound. You are actually unable to build the vehicle with both the Rebel 12 package and the 9 speaker package, as the 19-Speaker Harman Kardon® Premium Sound is already included in the Rebel 12 package.
The reason the 9 speaker system is showing is in case someone wants those speakers but doesn’t want the 12” Uconnect. If you are interested in purchasing this vehicle I would recommend visiting your local Ram dealer. "
I ended up finding a 95% match on a dealer lot instead. It has the "19" speaker system and I really enjoy it.
I'm pretty sure I've seen Rebels on YouTube or on dealer websites with a 12 inch screen and Alpine 9 speaker system. I wonder if in the past the Rebel 12 didn't include the 19 h/k system automatically.