In the second set of the Kaldesh Block, Aether Revolt, one card is Dark Intimations, which includes this text:
When you cast a Bolas planeswalker spell, exile Dark Intimations from your graveyard. That planeswalker enters the battlefield with an additional loyalty counter on it.
This is notable because there are no Bolas planeswalker cards in the entire Kaladesh block, so in a format that uses only cards from that block, such as Draft or Sealed, that ability has no effect. Even more broadly, while there is Nicol Bolas, Planeswalker, it was not printed in any Standard-legal sets as of when Aether Revolt was published.
Are there any other instances of this sort of thing in the history of Magic (excluding Time Spiral block, which was a block designed around referencing past and future Magic sets)?