It appears that there is no established name for this concept, but if you are looking for a suggestion, "potential covers" might be a reasonable name, since these are precisely the pairs $(x,y)$ which are not in the partial order $P$ but would be a cover in $P\cup \{(x,y)\}$.

EDIT: Whoops, sorry, this is nonsense. They need not be covers in the extension.

It appears that there is no established name for this concept, but if you are looking for a suggestion, "potential covers" might be a reasonable name, since these are precisely the pairs $(x,y)$ which are not in the partial order $P$ but would be a cover in $P\cup \{(x,y)\}$.