The study found small increases on some vehicles while others had decreases depending on the engine design. This is where the new study differs from the previous EPA study which was based on tests of only a single engine model that happened to show an increase. The EPA made a general conclusion about the effect of B20 based on a single data point. Based on this more complete study it appears that B20 has no real impact on NOx emissions overall. Good thing they retested. The full report from the study can be found here.
[Source: National Renewable Energy Laboratory]