But that's what I'm saying. If the scenario I said happened and the house leaders got spirited, we'd still be able to get the spirits Byleth came with, but swapping out the house leaders. And look at all the options that could've replaced them.
Hubert, Ferdinand, Linhardt, Caspar, Petra, Bernadetta, Dedue, Felix, Sylvain, Annette, Mercedes, Ashe, Lorenz, Lysithea, Marianne, Ignatz, Raphael, Leonie, Alois, Shamir, Hanneman, Manuela, Catherine, Cyril, Flayn, Jeritza, Gilbert, Yuri, Constance, Hapi, Balthus, and Three Houses!Anna.
And those are just the playable Three Houses characters who didn't get spirits. Not to mention Hilda, Dorothea, Ingrid, and Seteth wouldn't have gotten them in this hypothetical scenario either, so they'd be on the spirit table for Byleth too.
We don't know for certain if a second pass was originally planned, but it was absolutely known and finalized before the Sword and Shield spirit event released.