AFAIK nearly all data are anecdotal. The most compelling anecdote that I have read on this forum occurred about 6 months ago. A poster from the SF East bay area (much warmer than SF, though not as hot as Texas or Arizona). A member of this forum who works at a large East Bay firm that maintains an email list of electric cars for scheduling purposes of the limited charging stations at work, sent a query to the list members. He asked for degradation reports from people who had purchased late MY2012 Leafs and early MY2013 Leafs. The cars were only a few months apart in age. Several list members reported significant degradation of their 2012 Leafs, none of the 2013 owners reported any degradation. I have searched for that post on this forum, but can't find it.
We have 2 Leafs, both made May 2013. One has 15k miles, the other 12k miles. There is no degradation as measured by LeafSpy capacity or GIDS. I frequently drive mine below VLBW and mostly charge to 100%. I haven't done any recent formal range tests, but I still have no problem driving from Palo Alto, over the Santa Cruz mountains-hiway 17 to Santa Cruz and back on one charge. 84 miles. Palo Alto weather is warmer than San Francisco, but cooler than the East Bay.
This information, along with the remarkable lack of 2013 owners reporting bar loss, lead me to believe that the 2013 Leafs do indeed have more heat tolerant batteries than the 2011 and 2012 Leafs.
I actually think they may have the Lizard battery in them, but Nissan didn't announce that fact, due the the bad publicity of the battery problem of earlier Leafs. In other words, the 2013 and 2014 owners are the beta testers of the Lizard battery.
2 LEAFS, bought 1 week apart. 2013 S for me, 2013 SV is wife's. Both manufactured May 2013. I lost first bar at 36,000. Wife still has all bars at 50,000.