I think they are just planning to be a bit more strict.
In NH, the judges flunked my car, since for that race, I purchased wider tires.
I had narrower spares I put on the rear, and built out the front fenders at the track.
If you are building wider fenders, they need to be heavy gauge steel. In the rear, I plan on using a 55 gallon drum, as they suggested.
Flexible metal, like duct-work will not pass, neither will plastic/rubber.
They don't really like fenders attached with rivets...they prefer welded....but we used some heavy duty rivets...and it came out solid....and judges were happy.
The car in the photo definitely will not pass.
MarioKart Driving School: 1987 Honda Prelude Opus #28 (still can't win anything...)