No, it's very simple...far simpler than it ever has been (it must have changed in 10 or 11). An historical player is rated against his own league and time. It doesn't matter where you put him, he'll have those same ratings. So, Babe Ruth is still Babe Ruth in 2010.
Of course, it doesn't work exactly according to percentages. If he hit 54 HR in 1928 when HR's were about 35% of the 2009 average, then he should (in theory) hit about 154 HR's in 2010.
The league totals and modifiers and stuff will limit him. He's still only going to have a max rating in Power. So, it's not going to be ridiculous, but you should still see him as someone leading the league in HR's.
This is exciting, actually. I somehow missed that OOTP even did this kind of era adjustment. (I'm usually looking at online stuff when testing and don't do much more than dabble in historical.)
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