"The uncertain button should be used in cases where there is some evidence that connection might be true or even probably true, but there is still some doubt."
This makes a lot of sense to me - is there a policy that states this explicitly?
Converting this to percentage probability, that might mean something like this:
>95% ("reasonably certain") - Link parent, no comment
>50% - 80% ("probable") - Link parent, flag "uncertain"
20% - 50% ("possible") - Don't link parent, perhaps reference in the text as a possibility
<20% ("unlikely") - Don't reference in the text, but perhaps include in the research notes or comments if it is regularly linked on the internet.