Am I right that the question seems to hinge on what a re-roll is and when you can do it?
If that's the case the answer would seem to be undefined.
The question does indeed hinge on what a re-roll is and when you can do it. I personally see a reroll as changing the dice roll, and fail to see how it could be defined differently though it seems apparent that others do see it differently. I invite them to share their personal definitions so that we may discuss this further.
With my definition, because you can't change the past, I see the effect as a kind of triggered effect and the course of events would be as follows. The dice are rolled during the Roll Dice Step. This
triggers any potential reroll effects currently present. Once all rerolls have been made, the dice results have been
determined.Now, if a new potential reroll effect is put into play after the initial roll has been made, it does not get triggered and
can not change the past. This is different from Brace Yourself or Rhino Hide, because those affect how the dice are applied,
in the future. They don't affect the results of the dice themselves,
in the past. A Rhino Hide doesn't change the fact that you rolled 2 normal damage, it just prevents that damage from going through. This would be more similar to trying to reveal a Bear Strength after rolling your dice in order to add two more dice to it. That is what we're talking about after all, changing the dice roll, and after a result has been determined it is too late for you to change it.
Again, I invite others to share their definitions of a "reroll" that don't include changing the dice roll.
That sums it up. The issue in question can only happen once, if the card is revealed after the Roll Dice Step. Then the question becomes, does one a round mean only during the Dice Roll Step or can it be in between that step and the Damage and Effects step.
It is undefined as you stated, and I am afraid that we are going to revisit a lot of rulings around issues such as this.
That is not the question at all. The question is, when the card is revealed, can it change the past? The rules say specifically that it can not. Thus, it can affect a roll in progress, but not one that has already been determined.