Historical Rules · 7 August 2020
Rule 701.13d
Official source text from the 7 August 2020 Rules release
If an ability checks information about a single milled card but more than one card was milled, that ability refers to each of the milled cards. If that ability asks for any information about the milled card, such as a characteristic or converted mana cost, it gets multiple answers. If these answers are used to determine the value of a variable, the sum of the answers is used. If that ability performs any actions on “the” card, it performs that action on each milled card. If that ability performs any actions on “a” card, the controller of the ability chooses which card is affected.