If you were to compare the RPM gauge of your car to that of an aircraft engine it would be appropriate to say that where the red-line commences it would relate to 100% rpm; or where the manufacturer might give an appropriate guarantee that all will be well. A temporary overshoot into the red wouldn't do your car engine too much harm; the same applies to an aircraft engine. A Take-Off limit of, say, 110% for X minutes, would be much the same as saying that such a temporary overshoot is acceptable for the defined period.
Though, I'm dumbfounded to understand why the absolute maximum couldn't allways be 100%... wouldn't that make more sense?
TCF