Northern Tracker card text states: Response: After Northern Tracker commits to a quest, place 1 progress token on each location in the staging area.

My Question: Do you apply the progress tokens immediately when you exhaust this card to commit to the quest or at the end of the quest phase after you have added new cards to the staging area?

For example if there are two locations in the staging area at the start of the quest phase and perhaps four locations by the end due to two being added in a two player game, does each location get a progress token, or just the two that were present at the start of the quest phase?

You apply it immediately. Characters "commit to the quest" when they first exhaust, which is before encounter cards are revealed.

I'll just add that all characters a player choose to commit to quest are exhausted and commited at the same time.

Perfect. Thanks.