My recollection is thst Sprucegoose is right.
When Royces did the 211 G/H series 100% N1 was that which produced the rated thrust. They have since re-cored with a Trent derivation which produces its rated thrust at a slightly higher speed, hence the 104% or so values. Incidentally, the engines controllers lie to the airframe computers about exactly what speed they are doing. This means that the FMC still thinks 100% is the rated thrust rather than the 104% or so !
It saves having to reprogram the whole bloody lot.
VnV...