Correct, because the MC/IC Relationship throughline is about the RELATIONSHIP (e.g. Family, Marriage, etc.), not about the MC or the IC.
For example, you can imagine a conversation between two characters discussing the marriage between MC and IC:
BOB: I hear their marriage is pretty rocky.
SARAH: They're working on it.
BOB: Maybe . . . I saw them fighting at the restaurant last night.
SARAH: Over what?
BOB: I couldn't hear, but she went storming out and he just sat down and ordered another drink
That brief discussion is ALL about the relationship and its problems, yet neither the MC nor IC are in the discussion -- or named. Only the marriage is identified.