So a couple friends of mine got copies of Gears 3 early. I asked them if their unlocks worked ok and they both were missing 1 chrome weapon. One was missing the chrome retro (domination achievement) and the other was missing the chrome hammerburst (dirty dirty horde achievement). The problem is they both have those achievements. We did a little research and realized that both of them unlocked every chrome weapon who's achievement was TIMESTAMPED. While one friend unlocked the chrome retro (his domination was timestamped) the other did not (his wasn't). Same thing for their respective chrome hammerbursts.
Did Epic ever say you had to have timestamps on the chrome weapon achievements? I would think no considering most of the chrome achievements (especially those 2) were probably mostly done offline. Or maybe this is a known issue and Epic is working on an update for it. Anyway I figured I'd let you all know. And as of TU1 they still will not unlock correctly.
I already posted this thread in the main Gears of War 3 section, but I figure if its here it has a better chance of being seen and looked into.