You've got some good questions. I grew-up in the Catholic Faith and so this is all part of my home and it never occurs to me to question it.
It is only when Steve comes over to my house and says, "T'heck is the deal with that wall-hanging, the one of St. Francis with his wounds?...and I say, "oh, he received the Stigmata. He was the first one you know."
And you say to me, "well, I gotta get going..and you race out of the house...
Ha Ha Ha...I rarely do think about this. Obviously, one doesn't have to accept this as Doctrine, as least as far as I know, but it is just part of our Tradition and, thankfully, there are much smarter men here than me who can explain it to you. It was Chesterton who noted that many of us know these things in our hearts but it is really tough to put it into words.
I can see why another not raised in our family would be surprised at some of the things I take for granted.
I really have not studied the history of stigmata/stigmatics. My interest was peaked by the suggestion that Paul was a stigmata in this same sense. I questioned that because I was unaware of any biblical evidence. The discussion leaves me with the same conclusion. I also was not aware of any traditional evidence that Paul was a stigmatic and I have not been given any.
I was not aware of the timeline NYer and you posted. It immediately struck me as curious. There may not be an answer, but certainly Catholics have discussed it and offered opinions.
I do think outsiders ask questions that never occur to insiders. That's one reason I enjoy interaction with brand new Christians and non-Christians, they ask great questions.
Thanks for letting me come into your house and ask questions.