Can relinquished be special summoned from the graveyard?

Ritual monsters may only be special summoned from the graveyard if they were successfully summoned by Ritual Summon. If they were sent there in any other way - like simply discarded from hand, or improperly summoned by Ritual Foregone (it special summons but does not Ritual Summon), then you cannot revive them from the graveyard with cards like Monster Reborn or Fulfillment of the Contract.