I was going to write something else, but the concept of the Laws of Undocumented Personal Gnosis came up during the first one and seemed to be a much better topic than ranting about the Plastic Paddy Racist of the Month (Na Astaraichean, if you want to Google the loon).
The laws, in first draft:
1) No UPG is allowed to contradict known facts about the associated pagan culture and stand as more than a modern invention. It is also probably useless unless you don't care for accuracy.
2) If a UPG does not contradict known facts but cannot be verified within the same body of knowledge, it remains a modern invention. This does not mean it is useless.
3) If a UPG turns out to fit a gap in known tradition in a fashion that does not activate the first law, it is worth pursuing further.
4) If a UPG that meets the second or third law is arrived at by people who have had no real contact with each other, it remains modern but is Shared. This means the group just may be getting somewhere interesting.
5) If a UPG becomes a SPG and said SPG is adopted outside of the groups who first thought of it, it becomes a modern tradition.
6) There is no way for a UPG to become Ancient Lore unless it is kept mostly intact for at least 1,000 years.
Any refinements that y'all might want to suggest, leave them in comments. I'll be grateful.