I have an '00 Ebony and actually just noticed the other day that my registration and my insurance list it as an Ironman. Like others have said, I don't think it makes any difference in taxes or insurance coverage so I just let them (DMV and insurance company) wallow in their ignorance.
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless