These are relevant references from the Books where Plenipotentiary is mentioned.
I make no pronouncements on these matters, but report them as I find them.
Arrive at your own conclusions.
I wish you well,
"Behold Lord Grendel," said Decius Albus to the gathered assembly, indicating Kurik of Victoria, "ambassador and plenipotentiary of the great Ubar, Lord Arcesilaus, of rich Mytilene, amongst the Farther Islands, well beyond Cos and Tyros, come to establish ties of friendship and commerce between that great ubarate and our own glorious Ar."
Plunder of Gor Book 34 Page 433