Odd, it should not be critting at all (and I can't seem to manage to make it crit for me even with a 100% crit rate). Are you certain it's Vampiric Requiem that is critting?
As to the damage discrepancy, I took a deeper look at it and there's just something about the way the game rounds the numbers numbers that's causing it to be slightly off. Again, not sure there's anything I can do to fix it. The choker is pretty well balanced in its current form.
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