My understanding is that the 100% RPM value for an engine is the point at which the engine produces the ground level rated thrust and will do so all day if asked.
For those engines that allow in excess of 100% there will be some time limit defined by the engine manufacturer at which the engine may be run (beyond which damage may occur), which will produce some greater thrust value.
For example I believe the takeoff thrust setting for a 737NG is 101.5% N1.
- GY
P.S. There are certainly others who regularly contribute to this forum with more knowledge related to this topic area.