I'll take a stab at this...
The number was set based off of what we thought was the max leagal limit based on the 2011 rules.

So w/ the tire all the way out (on a stock OEM car - more than one car was measured) but with the top facing tread block still under the fender, we took that measurment and set a limit. I can tell you that the limit for 4th gens was set NARROWER than what my 4th gen could be set to under the 2011 version. So it is my understanding that the number is the limit and the limit should not require fender mods in order to get to the limit (except the Fox). Since the limit is set by a hard number, I can't see how anyone would be DQ'ed as a result of the tire not being covered by the fender as a result of crash damage. Fix said damage and the track still has the same limit.

Al's post on the National site is a result of some of the SN-95 guys saying the track limit for them sets the tires outside the fenders. Since this should not be possible if the numbers came from a "legal" car, we have to take a "time-out". So some time is being taken to see if this is true, and how these numbers came to be. It is possible we could revert back to the old rule for a short time until we get this worked out.

I hope I helped. Somehow, I don't think I did.