Does Commander Tax reset?
The commander tax never resets, but it also doesn't count times when it isn't cast from the command zone; so you must pay an additional {4} in your case.


  903.8. A player may cast a commander they own from the command zone. A commander cast from the command zone costs an additional {2} for each previous time the player casting it has cast it from the command zone that game. This additional cost is informally known as the “commander tax.”


The additional 2 per time it has been cast counts every time it is cast from the command zone.