My mistake on which year the redesigned Corolla came out.
The 2014 and 2015 Eco have the same ratings, but there are two entries for each at Fueleconomy.gov. One for the CVT, and the other for the CVT(two mode eco/normal). It appears to not be two different transmissions, but just the difference between normal and eco modes. It's 2mpg on the high way rating that brings down the combined one. I'm guessing normal is the default mode, which is what the EPA testing is done at, but Toyota submitted eco mode results for legal advertising.
Combined MPG for the line up; Eco 34/35, CVT non-eco 32, 4spd 31, manual 31.
The non-eco CVT also has two entries, normal and sport mode, but it is only one mpg on highway. The combined for the 4spd and CVT is close, but it appears to be a fluke of the city and highway averaging and rounding; the separate city and highway ratings are two mpg apart.