I figured you come out swinging
“Every institution has its own legacy policies…Concisely, you’d be wise to ascertain the legacy guidelines that apply at each of your applicable target schools.”
^^This is the most important part of your post, and one of the points the OP was asking about, and one of the pieces that I responded to.
Your link is interesting and confirms that every institution has it’s own legacy policies…but doesn’t back up your last two points, or even particularly contradict mine (except that they do specify grandparents as counting).