I’m sure you’re correct re those cases.
But, as I said, it’s not codified. It’s just “past practice” and can be changed.
It’s “past practice” that can be changed, but it can only be changed by the party that is nominating the VP candidate. Trump can’t change this practice on his own; the GOP leadership has to change it. Do you really think they will voluntarily surrender their power to select the VP candidate?