An effect that refers to a milled card can find that card in the zone it moved to from the library, as long as that zone is a public zone.
July 3, 2020 · Core Set 2021
rule 701.17c not present in this release
June 8, 2018 · Battlebond
If multiple players scry at once, each of those players looks at the top cards of their library at the same time. Those players decide in APNAP order (see rule 101.4) where to put those cards, then those cards move at the same time.
April 27, 2018 · Dominaria
rule 701.17c not present in this release
September 30, 2016 · Kaladesh
If a player is instructed to search a hidden zone for cards that match an undefined quality, that player may still search that zone but can’t find any cards.