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You can only negate things during the phase they occur in.REG: "Negating an artifact during battle does not go back and replay the whole turn as if the artifact was not there; it only negates the special ability of the artifact from the current phase forward." (Interrupt or Negate Last, Special Conditions)
When was it ruled? Not sure, probably a couple years ago, if not longer. An old version of the REG just said something about negating stuff from previous turns, I think.DoN can negate a prep phase action (like the first use of a Holy Grail) during the prep phase, a battle phase action during the battle phase (like Three Nails), etc.