A Merchant Seamans’ record on FindMyPast shows Charles Walters (born 1889 London) officially changed his name back to John Joseph George Thomas on 1 May 1940. As proof he produced his birth cert dated 25 March 1886 London. The record also states he “died in local hospital” on (looks like) 20 July 1940.
BIRTH: John Joseph G THOMAS Poplar, London 2Q Vol: 1C Page: 618, mmn KITTS
There is a John J G Thomas, single, with corresponding birth date recorded at Chertsey Surrey in 1939 working in an Airline Factory.
How did he get to Argentina, I wonder