Hilico,
This is always an interesting point. The concept that a limit must be 100% is the issue, because you are thinking the gauge is showing percent of the maximum. The gauge is actually showing percent of an arbitrary number (what is 326 rpm, or 826 degrees, after all?) and you must keep the needle below another arbitrary number.
The rotor is allowed to go to 115% power off, and can slip to 125% before maintenance action is required. Where do we declare 100%? which one? Good question.
Redesign of all the gauges is expensive, and not particularly necessary, mostly.