In the cases of the special elections in Davao del Sur and Davao Oriental, it was due to the creation of these new provinces from the original Davao province. The congressman from the old Davao's at-large congressional district was free to choose which province he'd continue as an incumbent on. Lorenzo Sarmiento chose to continue at Davao del Norte, another newly created province, necessitating special elections in the other two provinces.
The governor of undivided Davao province, Alejandro Almendras, supported Artemio Loyola, then switched his support to Vicente Duterte.[1] Duterte was then Secretary of General Services, had previously served as governor of Davao, and wanted to revive his political career, but was defeated by Loyola. Duterte died in 1968.[2]
1967 Davao del Sur's at-large congressional district special election
Incumbent Eladio Balite died in office on August 24, 1967. Balite himself entered Congress by winning a special election in 1955 for Samar's 1st congressional district, which would later be Northern Samar.
1967 Northern Samar's at-large congressional district special election