August 6, 1569 was the date of the confirmation of the position of Miguel Lopez de Legazpi as governor of Cebu in a royal cedula. More than four years before, on June 4, 1565, he and his men defeated the Indianized Rajahnate of Cebu under Rajah Tupas, who surrendered in a treaty, and from that date, they administered the areas under the control of the Rajahnate as “Cebu province”.
So technically, August 6, 1569 was not even the Spanish foundation of Cebu, but the Spanish government’s assent (ratification) to what its agents had done a few years before.
Celebrating the Spanish foundation of the province on August 6, 1569 instead of June 4, 1565, when it was actually founded as a Spanish-controlled area, is akin to saying that you only own a piece of land you have occupied for years from the time the government confirmed your title.
Moving the foundation date to June 4, 1565 will also clearly establish the continuity of the province of Cebu with the Rajahnate of Cebu.
(I understand that the extent of the territory of the Rajahnate of Cebu is very much less than the current extent of the territory of the Province of Cebu, but at the time of the Spanish conquest on June 4, 1565, what was referred to as province of Cebu was the extent of the territory of the Rajahnate of Cebu. Through the years what was referred to as Cebu province expanded, and there was even a time when Bohol was considered part of Cebu.)