Firstly, the confusion arise becoz me n tidusboi, we both do the vit0 trick, but then we DID NOT do 9999 damage afterwards, so we guess that there muz be some things that we do somewhere that causes the boss vitality to not become zero. Thank you for confirming that we cannot do armour break before vit0.
As in your question y I bring armour break when I wanna use vit0, it's becoz my team is able to defeat almost all of the boss w/o using vit0. So it has become 2nd nature to equip my team with power/magic/armour break as default abilities. So if I wan to make a quick decision, due to fun or time saving,to use vit0, I can straight away use it, thus bringing armour break into battle. Anyway I feel my skills slots r more than enuff so I'm not really wasting slots.
For Jenova birth, becoz I killed it rather easily using different skill, I didn't get the chance to use vit0 on it. So ur insight is quite informative.
From your narrative, can see you are quite a heavy user of vit0. From my mediocre knowledge from jap side is that there's new boss/es that haf 300k Hp. And with the removal of vit0 in Japan server, some player are finding it very difficult to deal with the boss. So I strongly encourage all bros here to rethink their battle strategy for the long run.
Once again, thank caim1984 for the confirmation.