I have a 2014 RDX Acura and cannot find in any Acura booklet at what percentage the oil must be changed if under one year since last change. Booklet says at least once a year.

The owner's manual is correct. Engine oil is shelf stable, however it begins to break down after being run even for a few thousand miles. Gas blow by, the unburned fuel that slips past the piston rings, while miniscule in today's modern engines do accumulate in the oil. This is the reason the factory for practically all brands recommend that the oil be replaced by the maintenance reminder or one year or so. To make it more confusing, there is a school of thought, that it can't hurt to change the oil than to wait for the mileage, as oil is less expensive than engine wear.

I go by the cars computer. When it says you're close. Make an appointment. Otherwise, oil doesn't go bad. It's not milk.