I can't say with certainty but I recall a couple years ago searching for the best price on one of these that they may have made a slight change in the design at some point and the packaging and designation changed a little as well and if anything would improve your shifting. Your old chain may be the older design and were still being sold as a not-so-old NOS. Notice there are different markings on the chains in your photos. Anyways just something to look into and I would contact KMC to confirm this. Also have you tried making any adjustments to the derailleur cable, might just need a little tweak.