It is forged and has a segmented A followed by a B.
The changes seem to be a slight improvement in that the surface area of the knobs that you would turn has been increased. Also I noticed that the A2 sight assembly is tighter and less canted to the side.
It is not a big deal, the finish is an exact match, (not that that matters either) I was just wanting to know.
Info like this can help you spot kit guns, and keep you from paying too much.
Since I ordered a BM M4 upper and got one, I have no complaint, I just asked for a CH and did not specify manufacture.