The other lieutenant-caused syndromes should be the same as that one. You must have been hit quite a few times, since as I recall, the rot doesn't proceed that quickly.
That is the odd thing. The rot is persistant. It never went away. You can test this by using
DFHack Full-Heal on him. Fast travel a few tiles and the rot begins again. If it is a permanent state, it must be somehow recorded and that is why it is strange to me that it doesn't appear in the list of active syndromes. He should have 11 active syndromes - one is Vampirism, 9 are various strains of necromancy, and is being a Fell One intelligent undead.
Now, from Legends Viewer, Moldath has
15 active interactions. Four of those are listed as intelligent undead "powers" which are active on him.
DEITY_CURSE_VAMPIRE_8 is fairly self explanatory - cursed by a god to be a vampire in a monastery.
The 9 secrets are the 9 flavours of necromancy Moldath has learned.
SECRET_UNDEAD_RES_40 is him being raised as a Fell One.
The ones I have highlighted in Red, which are not listed in any of the DFHack utilities, are the ones causing the issues.
Secret_98 relates to Gaunt Zombies, who Moldath fought in 807, and seemingly cursed him with Rot.
Secret_49 creates Empty Ones, who are very rare, as the slab that creates them was destroyed early in the succession game. I did find one of them in the ruins of Duskhome - Anir Pokedbent the Dimples of Dashing. Anir apparently casted Rot, Blister and Dizziness on him.
[OBJECT:INTERACTION]
[INTERACTION:SECRET_RES_POWER_98_1]
[GENERATED]
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[IT_MANUAL_INPUT:victim]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[IE_IMMEDIATE]
[SYNDROME]
[SYN_CONCENTRATION_ADDED:1000:0]
[CE_NECROSIS:SEV:500:PROB:100:START:0:PEAK:0:END:3:VASCULAR_ONLY:BP:BY_CATEGORY:ALL:ALL:RESISTABLE]
[OBJECT:INTERACTION]
[INTERACTION:SECRET_RES_POWER_49_3]
[GENERATED]
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[IT_MANUAL_INPUT:victim]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[IE_IMMEDIATE]
[SYNDROME]
[SYN_CONCENTRATION_ADDED:1000:0]
[CE_BLISTERS:SEV:500:PROB:100:START:0:PEAK:0:END:3:BP:BY_CATEGORY:ALL:SKIN:VASCULAR_ONLY:RESISTABLE]
[OBJECT:INTERACTION]
[INTERACTION:SECRET_RES_POWER_49_2]
[GENERATED]
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[IT_MANUAL_INPUT:victim]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[IE_IMMEDIATE]
[SYNDROME]
[SYN_CONCENTRATION_ADDED:1000:0]
[CE_NECROSIS:SEV:500:PROB:100:START:0:PEAK:0:END:3:VASCULAR_ONLY:BP:BY_CATEGORY:ALL:ALL:RESISTABLE]
[OBJECT:INTERACTION]
[INTERACTION:SECRET_RES_POWER_49_1]
[GENERATED]
[I_TARGET:A:CREATURE]
[IT_LOCATION:CONTEXT_CREATURE]
[IT_MANUAL_INPUT:victim]
[I_EFFECT:ADD_SYNDROME]
[IE_TARGET:A]
[IE_IMMEDIATE]
[SYNDROME]
[SYN_CONCENTRATION_ADDED:1000:0]
[CE_DIZZINESS:SEV:500:PROB:100:START:0:PEAK:0:END:3:RESISTABLE]
I think this is proof that these are the syndromes that are causing the rot, but doesn't explain why it persists and is still making him weaker by mangling body parts decades after it happened...