Yeah, I would think that I would have, considering I do after every level. I didnt notice I eve missed the achievement until looking back over the achievement list before starting up. But by that time, I was already in the next level. It may have not appeared in the normal collectibles because it is a secret special one? I am not sure man. Lol
Did you accept the mission overview or whatever? There is a screen that give you your level stats and collectable stats before you start the next mission. You just have to dashboard to start at your last checkpoint. You can also restart the level from there.