Do I need to change my oil when it is clean and full?

What is your question?

This is more of a general question. Suppose it's the recommended time to get an oil change, such as 3000 miles, 3 months, etc, but when you check your oil it is clean and full, as if it had already been changed. Is it still necessary to get an oil change? For more context, I have a 1990 g20 van with 102k miles. I got an oil change 5 months, 3000 miles ago, but the oil is clean and full. There are no leaks and the car runs well (I know, insane since it's 30 years old) just wondering if it's still necessary if the car seems fine.