If I understand correctly, some of the Xian miracle stories involve someone who prayed to a deceased “saint,” or at least asked the “saint” to pray on their behalf, who then claims to be miraculously healed.
Could G-d miraculously heal someone, even if that person never prayed to anyone, or even if that person did something they shouldn’t do (like praying to a dead person)? Of course — G-d can do anything. So it’s possible some of the miraculous recoveries really did happen. But we have no reason to believe that praying to that “saint” was the cause of the miracle.
It’s also quite possible they weren’t miracles at all. People are diagnosed with deadly diseases, which then inexplicably go away, all the time. Misdiagnosis could be the culprit. But the human body is also a mysterious thing. Some medical researchers believe, for example, that cancer is more common that we think, and that many, perhaps most people get cancer here and there, which then goes away on its own without causing any harm.