Interesting discussion, but just to be clear, I don't think any of this pertains to Kev1 and his aunt. With a modern saint like Pius X, I doubt there is a lot of monetary gain to be made in forging relics. I've heard there are people who are still forging things like "the true cross," "Mary's veil," and possibly more plausibly "St. Joseph," but even in these cases the documents look pretty obviously printed with some Microsoft Publisher template. I would say there is about zero possibility that this relic is a forgery, but I'm sure there are experts one could send pictures to. Now if the certificate claimed that his aunt had the head of John the Baptist, I'd wonder -- there are already three of those in the world. In the middle ages, most of the monetary significance of having a relic (and therefore the motivation for forgery) was the importance of pilgrimmage. Every village wanted its church to have a special relic to draw pilgrims for the tourist trade.
What is interesting to me is that the fact his aunt's mother had the document sort of suggests to me that she was the original recipient, or else that she got it as a gift from someone who was (like a priest). In my experience relics that are in the possession of individuals and have been handed on from person to person, usually don't still have the paperwork. Usually only the churches hang onto those. I wonder what was going on in her life in 1953 that would have resulted in her being gifted with that particular relic -- was it the name of her high school, or the church she was married in, or?