On May 26, 1966, British Guiana gained independence from the United Kingdom and was renamed Guyana.
Date of Issue: 26 May 1966 Topic: British Guiana
Description: 1966 Overprints of British Guiana stamps with “Guyana Independence 1966”
Watermark Multiple Crown & Script CA. By De La Rue.
GY #1-7; SC #1,1A,2-6; SG #378-84
Guyana Philatelic Society 
My collection if British Guiana stamps among them I have stamps in my collection more than a hundred years old.