If I cause a Deep Wound on an enemy and then do another Deep Wound while the first is still in effect, does the health reduction stack or does it still just count as one instance of DW?
If Deep Wounds works anything like spell effects, the effects of it do not stack, but the timer for how long it lasts is reset to the full amount (5 seconds, or whatever) when you apply it the second time.
It dosen't stack. If it did, you'd hear about tons of builds using multiple deep wounds. People would be sword/axe warriors and switch between weapons and inflict a series of deep wounds. It's a good thing it dosen't stack or warriors would be way overpowered.
There was a slight bug a while ago that pulled hidden stacks on DW, but that's long since gone.
But, like everyone else said, DW does not stack at the moment.
I don't know if it is an intended quirk or not, or even just my imagination but it seems the next hit after applying a deep wound is almost always a critical.