I had to test it today and although b-ref does display National Association statistics the same as major league stats, Immaculate Grid does side with MLB in not recognizing the NA as a major league. In other words, Cap Anson is a lifetime Cub despite his main b-ref page showing his years with Rockford and Philadelphia in the NA. However, even though MLB now recognizes the negro leagues as majors, I'm pretty sure I've gotten correct answers in the Immaculate Grid's "one team" category by using former negro leaguers who only played with one team after leaving the negro leagues… I'm certain I used Jim Gilliam for the Dodgers recently, though it's possible that was the Crossover Grid and maybe they could have different standards.