I found a book on Google books written by a Lt. Col St. Clair who was a soldier stationed in the British West Indies including Guyana in the 1830's. The opening of his book underscores the reason that The Venezuelan claim has no validity.
A Soldier's Recollections of the West Indies and America: With a Narrative of the Expedition to the island of Walcheren.
Lt. Col. St. Clair wrote this long before there was an official border dispute that needed arbitration.
The Pomeroon river was part of the Dutch colony of Essequibo and it was ceded to the British. A fort was erected at the mouth of the Pomeroon and what separated the fort and edge of settlement on the
Pomeroon and A Spanish Fort on the banks of the Orinico Delta somewhere, was wild uninhabited county where nobody lived but Amerindians.
Hence, my position that if the Venezuelans want to renegotiate a border between what is now Guyana and Venezuela, the line would need to be drawn somewhere in this formerly wild, uninhabited country. The Essequibo is not and never was the line between Spanish and Dutch settlement. The Essequibo claim, however dormant right now, is one that they purposely drew up in order to go into negotiations, at the turn of the last century, knowing that most of their claim would be arbitrated away by a third party. It was just a unfounded as Britain's claim to much of what is now the state of Bolivar in Venezuela.
The one word that shreds the Venezuelans mis-informed 20th century re-claim of Guyanese land is: 'Pomeroon'