MICHAEL_61: Very interesting. My conclusion: in order to buy a lens, get as many copies as you possibly can tested on your camera (preferably 10 at least) to choose the best one of them.
Well TomB and JonF, half of the four Canon "L" lenses I've owned in past years were clearly defective from the get-go (17-40 and 24-105), with a distinctly soft side seen (but only if you looked!) in prints larger than 8.5x11, and above 4x mag. on the LCD - pixel-peeping, if you wish. My Nikon F lenses of the 60's were much more uniform in their quality as seen in my 16x20 B&W's.
Not to care at all about taking the minimal time it takes to look for lens softness is kinda like the lazy woodcarver who never sharpens his tools, and tolerates the rough outcome as "the nature of the wood", or other such drivel.
Pro or not, you folks admittedly don't look very closely and must not print very large, deal with picky photo editors (that would be all of them), or have been jackpot lucky with all your lenses - a most unlikely situation...