How did Irons lead the team in YPC if he didn't possess certain knowledge?...
He didn't. Actually Hardy did. But, as discussed many times, Irons had a had yards/carry number because he played mostly late in games, in clean-up time. His yards/carry were actually very low when he played against first team defenses. In fact, if I recall correctly, he was the lowest on the team.
That was then, this is now. What will he do this year? I expect him to earn a lot more playing time in 2016.