They say you can't get more than fifty IBU into a brew that's still hot, no matter how much you add ... and that you have to hop-after flame-out to get increases beyond that ... and then it decreases over time too, in bottle, I guess ...
So ... I find it kind of humorous that people would list it ... because a) the measurement is not based on sound science to begin with, b) the amount they put in doesn't really mean it's there when you get it ...
This dude's studied the crap out of it, I guess:
http://www.monmouthcollege.edu/academics/faculty.aspx?id=0405052