One may assume that a mursal narration omits only a Companion. Yet Successors sometimes received reports from other Successors, and additional intermediaries may be involved.
Possibility 1: the Successor heard a Companion but left the Companion unnamed.
Possibility 2: the Successor heard another Successor who narrated from a Companion.
Possibility 3: more than one intermediary was omitted.
Consequently, the accepted integrity of the Companions does not resolve the separate question of an unknown omitted Successor or another transmitter. This possibility is a central reason that the probative value of mursal reports is disputed.