There is not. Norton was pretty much the punching bag to the elite aside from that win over Ali. Personally, I don't see it as miles off from what occurred with Tyson and Douglas. Sometimes a guy just has your number and that was the case with Norton over Ali. Norton never replicated that success, not even against lesser guys than Ali.
People don't like to hear it because of the love for that particular era but it is what it is. No one likes to think that someone that wasn't really that special managed to beat Muhammad Ali. Its not different than people who insist Douglas got a long count or that Lewis didn't take McCall seriously. In this case, they say a fighter who was actually mediocre at best was actually not mediocre but a very special talent.