Last year and this year 6920 models I had seen at the gun shop they're exactly the same as the 2013 configuration with Magpul MBUS2 folding rear sight, the front sling swivel are mounted at the bottom of the front sight base sling swivel mount, and standard M4 waffle type buttstocks.
I used to have a 6920 2012 configuration slightly different with detachable carry handle, side barrel mounted front sling mount, Colt Defense-Rogers SuperStoc, and the accessories package are also different with a heavy duty push button sling swivel, two Colt 20 rd aluminum mags, cleaning brushes (barrel and chamber brush), sectioned steel cleaning rods, basic black nylon webbing sling with two black metal buckles and owner's manual.
I also have an older 6920 2011 configuration and it's marked differently "Sporter M4 Carbine" with no caliber markings, they're similar with the 2012 configuration with the exception that it had the standard M4 buttstock.
I agree, most of my current four Colt AR and what I had before had the MPC bolt markings, there were some owners that reported only "C" markings instead of MPC, and there are some other different older ones with another letter batch code after MPC, there are also different markings from Colt of Canada.
On your 2014 6920 did you still have the heavy duty push button sling swivel included in your accessory package?