I've never returned any of my lenses for a new copy. I rarely even test them to the degree that many seem to. I take a bunch of test shots before buying, but that's pretty much it. I have the first versions of the 24-70 2.8, 70-200 2.8, and have owned at one point several other L lenses, and honestly, I know I didn't have a "bad" copy, but I couldn't tell you if it was good, or just average or whatever. I've never noticed a problem and either has anyone else. Maybe I'm lucky, idk.