Arris SB6190 / Baton Rouge, LA / Only 12 Channels

" I'm thinking either it was provisioned incorrectly"

Provisioning has nothing to do with channel bonding unfortunately. That's all done in DOCSIS negotiations before the config file is considered. IE you can hook up a D3 modem without a account and it will bond to what ever the lowest capability is between modem and CMTS. 

"Has anyone else experienced the modem not getting 24 channels when they are actually available? "

Can't speak from personal experience, but as per this DSLR thread, 12 channels was max in January in LA. End of thread mentions date of 3rd quarter of 2016 as possible node improvement, but that could just be for thread's OP local area. Brass tacks is modem connects at max available. As long as you have decent signal levels, what you get is what you get. Here is thread of someone with even problematic signal who is getting 24 channels down with SB6190 in CA. Who told you area had 24? I wonder if a sales rep saw that the suggested gateway for Ultimate in that area is 24 channel capable and just assumed area must be. 

It was a person from sales that mentioned 24 being available in the area when I inquired about the advertised 200Mbps down for the area and they mentioned I would need one of the newer Cox modems to get 24 channels as the SB6183's max was 12. So yeah, seems like your assumption about that is more  than likely correct so I'll probably just return the modem and put back the SB6183.

Additionally, researching now it would seem like 12 channels should be plenty enough to hit 200Mbps though I assume it would have to be perfect circumstances to hit it. 

Just a quick update. The tech visiting to check my problem says he get's 24 channels when he connects and says that I should be getting the same, but that otherwise all levels look good. I'm going to go buy one of the modem's directly from Cox and see if it makes a difference.