Okay, first, your knobs don't look like mine because the rubber ring and the plastic inserts are missing. Trust me they look just like mine before I added them. Here's a poor picture of my rear window defroster knob and lighter before I added them.
As far as the other knob, I can't say for sure but if you check the PET they list what I would think are all of the plastic inserts for the knobs that are available.
The list is:
Optional heater
Rear window heating
Illumination
cigarette lighter
fog lamp
Hazard warning light switch
radio
You can rule out the rear window heating and fog lights since you already have them accounted for. It's not the illumination, and I doubt is has anything to do with the radio. If you also have hazard lights accounted for then it must be the optional heater.