I see nothing wrong with uncertainty where manuports are concerned. It's the nature of many types of manuports to occupy an uncertain status. By definition, manuports are objects transported to a site, but not altered for use as tools. Some manuports can be recognized as connected to human activity. I find graphite at one site. It shows extraction of the graphite, by gouging or scratching. It's not a tool, just raw material. But, it would not be found at the site naturally, I know where the graphite was quarried, it's a manuport. I can be certain it's a manuport.
Same field gave up a split cobble containing a fossil fern impression. Extremely few rocks in the field. Which is unusual, our soils are pretty rocky. It could have been split open naturally, I find them like that on rocky beaches sometimes. But how did it get in this field? Dropped by the retreating ice sheet? Sure, why not? Glacial cobbles everywhere. Of course. But, this field has so few rocks, and lots of artifacts, multicomponent. Maybe a native collected this fossil and transported it to camp. A friend found a split shale pebble, fossil inside, and notched to form a pendent. So, I guess they noticed fossils. Well, of course they did.
So, I labeled that rock, and it's part of the assemblage from that field. I consider it a manuport. But, I do not ask for or expect certainty.
I cannot have certainty, and I am fine with that. I'm fine with "it might be a manuport". I see nothing wrong with uncertainty where manuports are concerned. The body of evidence can lean heavily toward transported by a human, but unless it shows extraction, or utilization, it's more likely then not that it will always carry some degree of uncertainty. What's wrong with that, anyway?
These kind of calls are best left to the person or persons who best know the site where found. The degree of certainty is theirs to decide I believe. I don't insist that anyone else agree my fossil fern is a manuport. I can't even be certain. And I have never even been to the site discussed in this thread. It's not an artifact, not altered that I can see, so the finder can make the call on manuport.