Ah, I have found something that makes my examples above wrong, for the mon mothma stuff.
Jabba's lead reduces damage by 30%. That's all calculating is done, defence, other bonuses etc, then the final damage number is decreased by 30%. My assumption, because I can't see the datacron code like I can see Jabba's on gg, is the datacron is the same as that, and it acts on the same number that the jabba damage decrease is on.
Mon mothma -90% or-45% actually applies to the offense stat of the character, rather than the damage. So the offense then has the damage multiplier of the ability applied, the defense of the target mitigates it, then we have a damage figure. At that point Jabba would take 30% off that damage figure (and so would the datacron take off 75%).
