We are from Buenos Aires and were surprised to see your messages. We´ve got a quite complete story about the origins of our family and want to share with you. The first Guedes were from Crestuma city, Portugal. Their names: José de Couto Guedes (complete surname, then simplified) and Francisca Javier de Olivera. their son, Jacinto de Couto Guedes and his wife María Fidel Bengochea came to Argentina and married in 1848. He died in 1876. They settled down in San Fernando, Buenos Aires Province.
We also have information about our "surname shield"... could see if it´s similar to yours.
Hope to have news from you.
Guedes Family (does anybody speak spanish?)