You can't really verify that it's a genuine Colt detachable carry handle from the forging marks because other manufacturers also use the same raw forgings manufacturers, most manufacturers like Colt final machines the raw forgings.
I have four (but gave one to my son last Feb.) an older made in 2002 which came with my 6721 carbine (HBAR heavy profile 1/9 twist barrel) that's marked "A-9" (the letter A is actually splintered A forged by Anchor Harvey) but it have a very rough forge flash inside of the carry handle, then I have 3 with smooth forge flash with my newer 6721 in 2010, a SP6920 "Sporter M4 Carbine" marked, and a LE6920 "M4 Carbine" marked (gave this to my son), all these later three had the square forge marks from Brass Aluminum Forging Enterprises, and all these last three I opened the factory carbine box with the factory seals at my dealer when I picked them up.
I also took apart the peep sight and the leaf spring under the peep sight of my older "A-9" marked carry handle and there was a "H" letter mark, which might not be a genuine Colt (the letter H a factory batch code or does it mean Hesse or High Standard, etc.?).
The only way I know how to get a genuine part is to get it from a reputable Colt dealer like Brownells or Specialized Armament Warehouse, etc, but it would cost a more.