I dont think it has anything to do with holding the button at all.
My understanding of it is
I think there is time frame where scaling is locked on lockable moves. Also, mutliple hits like karate / ryo / roberts fbf moves arent scaled per hit, since all the hits are considered "1 move". Which is why you wont see the damage decreases as the punches / kicks keep hitting.
kim combos
It says that "if you activate another move that shares "scale lock" in quick succession you deal the damage based of the last move made". It exactly how its said. Both DM are scale locked moves so doing them in quick succession nets you unscaled damage. Do it slower and "scale locked" is lost, which is why its 10% less in hits. The combo with cB into DM, the cB is not a scaled locked move which is why, regardless of how quick you connect DM, its already lost 10% per hit.
benimaru combos
first combo - dp+B/D (scaled), air qcf+A/C (scaled), qcf+A/C (scaled), DM (Scale locked) SDM (Scaled locked)
second combo - cB x3 (scaled), SDM
It saying taht even tho the first combo had more hits cos of the DM, the scaling is the same as if it was cB x3 because the DM was locked at the 3rd scale and since the SDM was done quick, it was also scaled locked.
Terry / Ash combos
Self explanatory. Basically saying that all the moves / DM linked together are not scaled because the of the previous move and the next move is done in quick succession.
eliz combo
self explanatory. her NM isnt scaled since it came from a DM, and the follow up DM isnt scaled from the NM, but the last DM isnt.
Idk if i explained it well enough, it makes sense in my head...