Concentric, it says "an overall transmission efficiency up to 96.5% at min cruise power (LoL test condition)".
A couple things to consider with this claim. What losses are included in that overall efficiency number? Were the oil pumps not operational? At what point during the LoL test was that peak efficiency number recorded? Having little oil flow within the gearbox housing would result in reduced gear windage losses and lower viscous losses in the rolling element bearings, at least during the very early stage of the testing.
One unusual thing about the overall efficiency of rotorcraft main gearboxes is the effect load has. Most MRGB losses are two types. Speed dependent and load dependent. For example, rolling element bearings have both viscous (oil churning) losses which are primarily speed dependent, and contact losses (sliding, skidding, etc) which are more load dependent. If the MRGB is operated at max speed and low load, the speed dependent losses remain high and only the load dependent losses drop. And a rotorcraft MRGB driven by turboshaft engines typically operates within a very narrow speed range close to maximum, with the input gear stages turning at high speeds.
With this in mind, it becomes apparent that if you compare two MRGBs operating at the same speed, but one at high load and one at low load, the one at high load should have better overall efficiency. If the 96.5% efficiency at cruise power number in that presentation was recorded at the end of a LoL test, that would be very impressive. And would indicate that the gearbox suffered very little damage during the test.