This is my opinion no. The Enchantment will always happen like a Enthunder and such. But the Additional effect wont always happen. Take it for what u will.
Most likely these effects will stack. When you hit something with a weaken defense status, their defense continues to fall each time the effect activates. Acid Bolts for example keep pelting an IT enemy with these and their defence will fall till they are no more harder to damage than a regular DC or EM enemy.
I've never heard that effects on status bolts stack. I was under the impression that once you read "so and so's defense is weakened" it doesn't get any weaker than that first hit. I know that you can get that effect time and again, but alls I thought was that it is resetting the effect each time. Does anyone else have any info regarding this? Being a soloing THF/RNG this is vital info to me.
The acid bolts reset their drop in defense each time they succeed. They don't actually stack. Much like if a whm casts barfire on you multiple times. Each time you will recieve the effect, however, it will not stack, the previous effect will be dropped, and the new effect will be added. The benefit to that is that it resets the duration inwhich the mob will be weakened.
So, with this dagger, you will only decrease the defense once, however, it will keep procing and keep it down for some time (I do not know how long the en-effect lasts, but typically the down effect will last one minute after the last successful proc.