Absolutely, as long as you know it to be a fact.
If you cannot prove it to be a fact but say you do know it as a fact then you either prove it or accept the other party has every right to dismiss it or question it and not have to accept what you say.
On the flip side, someone can accept your story as fact and they can use it to relay that to someone else, in which case they are appealing to authority (you) and expecting the person they tell to also accept what they accepted as their fact, from you. Also, appeal to authority.
If you started that story on your own then you are obliged to back up what you say or claim what you say is based on your theory and isn't actually something you can actually physically prove.
As long as you don't offer something as factual then nobody can expect you to offer physical proof, obviously.
It all comes down to whether you can offer logical reasoning that the other party can be left to ponder over, then it comes down to a choice to take whatever side offers the most reasonable outcome.
I'll discuss anything.
Just remember that many of you don't make something factual and do not ever be under any assumption that I'll follow a party line I do not believe to be using facts.
It's your choice whether you want to deal with me and your choice in what way you feel comfortable dealing with me. I'm just me and I'll take whatever comes my way no matter what is used to twist or deflect.