Yeah, they never intended the chemistry for the extreme southwestern US environment. The production design included an aging process that was supposed to minimize initial degradation but it wasn’t enough without active cooling, even in a pouch design.
Around mid 2014 a chemistry change was made that was intended to alleviate some of the issues, and a fair number of US packs were replaced under warranty.
Through design changes for the 64kWh packs for the newer models, they were insisting active cooling still wasn’t needed, so out they went, still sealed up without any cooling system, but I haven’t looked them up to see how well they’ve been faring since they dumped the production to a Chinese company.