Speedo Bezel/Gauge

So I was looking through pictures and have been trying to figure this out...

On the spedo where it says one of two things "Premium Unleaded Only" or "Unleaded Only" im trying to figure out where the year-shift was, if it was based on year, or was it based on Fed Spec vs Cali Spec? Or was it a mix of NA vs TT?

I've found that 100% of all Cali 1st gens are all "PUO" in both NA and TT only. Now head out of the Peoples Socialist Republik of Kalifornication and i notice a drop to just TT's with the "PUO" label.

Any insights? I also notice its also due to gauge swapping to make it a lower milage car even though i know later gens were "UO" even in the TT form.

-dLs-

It has to do with the timing maps on the ECU for that vehicle. If you put 86 octane in a Cali Spec NA, it wont pass inspection, and has a good chance of spark knocking.

Okay thats what i was trying to figure out. I wasnt 100% sure. But its weird that i find that some 1st gens have the "UO" in it from cali and the same year had "PUO" in it as well, leads me to believe that was a swapped bezel.

-dLs-

Fact of the matter is ALL DOHC's recommend Premium Fuel. Even though it doesn't say it on 91's dashes, it does say it on the gas lid. Also 86 octane will not cause an emission failure. 87 octane is not any dirtier to burn than 93 octane. One just has more knock preventer (octane) in it.

So only 91's only say Unleaded Only on the dash. 92-99 all say Premium Unleaded, unless its a SOHC.

And Fed Spec and Cali spec has nothing to do with where the car came from. My car never spent a minute of its life in Cali and its Cali spec. Its all about the factory emissions equipment.

I'm drawing a blank, I don't recall seeing that wording anywhere on my gauges, only in the gas tank door?

Its on the tach.