It applies to Mary's womb. As I said, where God dwells in Person is Holy of Holies. In order for her to have other children, that Holy of Holies would have to be occupied by ordinary humans.
Jesus dwelt in the house of Mary and Joseph, thus apparently making it a Holy of Holies. Were all visitors vaporized at the doorstep? Wouldn't the ordinary human Joseph have been killed instantly, and contrary to scripture? :)
In addition, if Mary's womb was a Holy of Holies, then wasn't it made unclean every month during Mary's period? It seems to me that if a pass can be granted there, then a pass can be granted for the BLESSINGS of Mary's other children.