Over the past several years I've bought/sold more camera systems than I care to remember (I finally decided to stop this year after losing a chunk of change selling my D610). I switched in/out/in of Micro 4/3 a few times (E-PL5, E-P5, and now the E-M10). Looking at my Lightroom catalog and comparing serial numbers, I realized I used 4 copies of the Olympus 17mm f/1.8 and 4 copies of the 45mm f/1.8 (most were sold, a couple were returned for defects). I always thought the 17mm f/1.8 was different from the other Oly primes I've owned (12/25/45/75) in that it was somewhat soft wide open but with smoother OOF rendering, but became sharper stopped down. Most of the reviews on the web seemed to confirm this. I never thought any of my 17mm were soft or 'different'. That was until I bought my newest copy of the 17mm, which is tack sharp wide open in the center. It seems to have a bit more field curvature than my previous copies, which means a bit more OOF corners shooting stopped down for landscape, and there is a slight bit of decentering, but since I normally use this lens for environmental portraiture it was a welcome trade-off. Conversely, the last two 45mm lenses I bought seem to be noticeably softer wide open (and until about f/2.8) than my first two copies, especially at medium to long distances. There seems to be some longitudinal CA that makes fine details hazy. Both of these lenses have pretty close serial numbering and were made in Vietnam vs. the older lenses made in China. I don't know if that means anything. I've returned the last 45mm I bought for an exchange to see if I can get a better copy. I also used two copies of the Olympus 12mm, one that was terrible at all apertures and the second that was sharp. Certainly Olympus isn't the only company prone to this - I've had the same issue with Canon, Nikon, Sony, Sigma and Tamron (and haven't tried Fuji, but I'm sure they're the same). With cameras only continuing to increase in resolution, I think companies also need to focus more on the lens side of the equation for QC.