"I would have thought that would cause jay’s preset to show a red cell if any underlying patches or samples were missing."
If they play, you own them. You bought them in the Brass II bundle (or you bought them separately). I don't use the Epic Orchestra either. (Yes, "Epic" in this sense is confusing.)
Keyswitch-specific sequences. I understand. That's why my suggestion was a diagnostic, not a solution. As such, it still may be helpful for you to load 65 Horns - a8 > 01 HO-8 Preset VIPRO and compare behaviors.
But when I looked, I could find no setting that caused one to behave and the other to mis-fire. To my ears, the "bad" cell sounded like it was running out of voices -- but how can that be when it's using so few voices?
Does Jay's sequence use the cell in question for repetition?