The last 6920 that I bought was early 2012 (about April) when the first "M4 Carbine" markings was released, it had a detachable carry handle and Colt Defense-Rogers SuperStoc, and the box had the blue label not the 2013 config. white label, my serial number is LE105XXX.
It also have the barrel mounted side sling mount, by the 2013 configuration they changed the front sling mount attached to the bottom rear of the FSB.
Another change to the 2013 model was the Magpul MBUS2 rear folding BUIS, instead of the detachable carry handle, maybe the one you saw was a very early 2013 model that was released late in 2012.
The accessories package had the two 20 rd Colt marked aluminum mags, cleaning kit, basic black nylon sling with two black metal buckles, a heavy duty push button sling swivel with a flat smooth button, and of course the owner's manual.