Search Google for engine knocking and you find tons of material that state "Knocking can damage the surface of the piston, the cylinder walls or the crankshaft bearings". Although ECU may adjust the fuel mixture to correct the knocking but still knocking happens by using lower octane. To me as a risk-averse guy, I prefer to continue using 91.

 

My 2017 Acura RDX Owner's Guide states: Use of unleaded gasoline of 91 octane or higher is recommended.

Key word is "recommended" and they are basing that on every single driving condition otherwise the Owners Guide would be 10X as thick.

It would be nice to have a "knock counter" because I would bet good money mine has not knocked at all based on my driving conditions. I might just get my Launch diagnostic tester out to see if it records that.

My neighbor who bought a new TL-S back in the early 2000s used nothing but Regular and damn, that car is still around in his daughter's hands...20 years later, and according to him, it required Premium.