Are the +1 threat for each warg enemy, that Northern Warg gives when revealed, given to only the wargs in the staging area at the point then that card is revealed, or also give +1 threat to wargs revealed later during the phase.
The ruling on effects like this has gone back and forth a couple times, causing confusion. But the latest FAQ (1.8) says in section 1.55:
FAQ 1.55 wrote:
A lasting effect created by an encounter card ability is recalculated if the game state changes.
So when a Northern Warg is revealed, it creates a lasting effect that gives +1 threat to all Warg enemies. If another Warg enemy is revealed later, that lasting effect is recalculated, which causes that new Warg enemy to also be included in the +1 threat effect.
And if TWO Northern Wargs are revealed in the same turn, they EACH give a +1 threat to all Warg enemies, which stack for a total of +2 threat on each Warg.