The thing to remember is that owner’s manuals are just one point in time. Things can change and they’ll never send out updates for a ten year old manual. Sometimes the manufacturer’s sites will provide the updates there or in their Q&A if they have one. That’s what Briggs did with oil anyway. Even in car factory manuals there can be out of date information that only the factory mechanics know about.
Edit: I just got gas a little while ago and noted again the premium pump had the non-oxy label on it. The label said for boats, antique cars, small engines, ATVs, off road vehicles, etc. Who am I to argue with a label? I don’t know what the octane rating is but I’ll just continue doing what has worked for me over the past ten years. Your results may vary as the finance guys say.