There is no difference in the question types of these three tests.
In 2011 the publisher of this test came out with the second version of the test so that they could update the norm tables used in assessing the scores of students across the U.S. They wanted to expand the age groups down to 4 year of age and up to 18 years of age.
The various types of scores utilized in the NNAT2 2011 updated norms are the same as those provided by the previous edition. There were no changes in the test items, scoring methods, score flow, the methods used to derive different types of scores, or the potential use and interpretation of the scores. The only change is the updated norm tables for deriving the NNAT2 Naglieri Ability Index (NAI). When using NNAT2 for the extended ages, Level A should be used for 4 year olds, and Level G should serve for 18 year olds.
The third edition of the NNAT, the NNAT3, was launched in the spring of 2016. The main differences between the NNAT2 and the NNAT3 are the rollout of new norm data for scoring and new administration options for online administration.