There’s one rule among many which communities use to engender trust within oral traditions. It is, said plainly, do not say anything that you do not know for sure.
What does that really mean? It means that embellishment is not allowed. Exaggeration is not allowed. Outright lying is of course not allowed. What about inference? Not if it is stated without qualification.
That is, if you know particular parts of a story to be true but not others, tell only the true parts. If you are asked about the other parts, simply say you don’t know.
If an accumulation of sources allow you to piece together a part that you hadn't previously known, SITE YOUR SOURCES!!
The telling of observed truth, the quoting and siting sources, the leaving out of gossip, all engender trust. And trust is the only thing that can form bonds strong enough for a tradition to flow over - from one person to the next, across generations and geography.