Most of his playing career, a ground rule double was counted as a homerun: http://en.wikipedia.org/wiki/Ground_rule_double

Since there is no way to go back and investigate, is it fair to say that some of those 714 homeruns would not have counted by today's standards. And I'm not even going to get into the tired pitcher era when pitchers routinely pitched complete games on sore arms.

Just something to think about.