Olives would continue to acidify after being pulled off from its branch, even after they have been turned into oil. This process could be observed on any other living plant as a putrefaction symptom. Light, temperature, air and time could only accelerate this process and storing the olive oil in the best way possible would decelerate this process to keep your product fresh for longer.
The recommended shelf life is 2 years for an unopened olive oil container. However, you can keep the olive oil after the expiry date that is written on the container, as there is no set expiration date for olive oil. Going past the expiration date only decreases its nutritional value and quality. This would cause the olive oil to taste more bitter however it is not harmful. Therefore you don’t have to throw away olive oil because the expiration date has passed, however keep in mind that you should not expect the values on the container to remain the same.