Historical Rules · 29 April 2022
Rule 702.124d
Official source text from the 29 April 2022 Rules release
Except for determining the color identity of your commander, the two commanders function independently. When casting a commander with partner, ignore how many times your other commander has been cast (see rule 903.8). When determining whether a player has been dealt 21 or more combat damage by the same commander, consider damage from each of your two commanders separately (see rule 903.10a).