Why does the N1 on a FJ 44-2A turbofan go to 104.4%?
100% is the designed speed - sometimes it can be proven, that slightly more is still safe to operate on. Now: Change all scales, so that the new full power is once again 100% - or allow more than 100% on the scale? As a matter of fact, this is much easier to do, as the software does not have to be changed a lot, dependencies to other components are still valid, the recertification mostly is also easier, ... This also has been done for the Space Shuttle Main engines, routinely operating at >100% nominal ( = design) thrust.