In reviewing the all Americans by year, none of the champions from 1928 were AA in 1929 so it was only 4 in 1929. And I was wrong in my statement about only looking backwards. Someone on the roster not winning in 1928 but winning in 1929 would count towards the 1928 team. Without having rosters it would be hard to decipher unless they AA'ed.
Some other random freshman stuff:
Only four freshman have won a national championship - Hutton, Smith, Branch, and Rosholt.
Only 32 freshmen has AA'ed and only 8 since 2000 - Thompson, Lewis, Rosholt, Hendricks, Friskhorn, Scott, Oliver, and Dieringer. All of them red shirted except for Scott.
Only 16 freshmen have won a conference championship and only 8 since 2000 - Lewis, Thompson, Morgan, Scott, Oliver, Perry, Dieringer, and Klimara. Morgan, Scott, and Klimara were the only true freshmen.