As far as I know it was me who first discovered the chemistry change in 2013 builds. Someone was posting auction data in the Fall of 2016, IIRC, that happened to list capacity bars and build months, among other data. I noticed that the only 2013 Leafs with two or more bars gone at that time were listed as having build dates January through March of that year. There were also few if any 12 bar cars listed for those build months. I found it very interesting, and some of us started to ask those reporting capacity loss (or no capacity loss) what their car's build date was. So far there have only been two exceptions - early 2013 Leafs with all 12 bars. Both were in or from cool climates. I also don't believe we've see any built later than 3/13 with fewer than 11 bars, although that is bound to change this Summer. I'd consider the evidence anecdotal at best, were it not so consistent. Since we know that the pack case design changed when production was moved to Smyrna for the slightly-refreshed 2013 Leaf, it can be deduced (although Nissan has never, as Cwerdna wrote, produced a scrap of information) that it was the battery chemistry that changed, rather than the physical layout of the packs.