Hello - I’ve just stumbled across this information when researching Lady Mary. Thomas is also my 13th GGfather. However I too am stumbling over the Stafford / Buckingham connection. Is it possible that Thomas was the Dukes illegitimate son - hence the surname? I know that was something done back then (giving the title as a surname to illegitimate children) however the Duke never admitted to Thomas officially in records discovered - so far!
He did however have a daughter Mary. Her name was Mary Stafford - who married into the Neville Family so I don’t believe she is the Buckingham connection. Mary Chaunter is someone different - It’s all very fascinating!