Dictionary definition: if what you are saying is equivalent to the dictionary definition of a term, its not UPG. Because the dictionary has verified it.
My opinion: I think this about a practice or figure in paganism or witchcraft of magic—but I did not gain it from inspiration from the gods. So it is unverified, but it is not “gnosis” in the sense of coming from the divine.
From folklore/myth/history: this is attested to in the folklore, mythology, history books, or what have you. Therefore it is verified and not UPG.
The mysteries: these are aspects of a mystical tradition that most people who explore the tradition realize in an epiphany, during an initiation ritual, or after time practicing. It is verified among other members of the tradition who have also experienced those mysteries. Reconstruction traditions are not usually mystery traditions persay. Although the traditions they are based on may have been.
Personal Experiences had in the otherworld/visions that fit within the generally expected: If you had an otherworldly or meditative experience that does not add new “facts” about gods or mythical places. Then its an experience not “gnosis” and there is nothing unusual asserted to be verified.
I adapted this from historical or mythological practices and I liked it: again here you are not asserting anything about the gods or otherworld or anything here and it wasn’t gnosis.
Most pagan and witchcraft traditions are not reconstructionalist traditions, the usage of the term UPG becoming less useful outside them. Another more accurate phrase being more useful to facilitate understanding.