I think the octane number is the measure of knock resistance of the fuel, independent of the engine it is used in. No doubt deposits cause combustion problems, but the introduction of oil does not lower the octane rating of the fuel whatsoever. The linked article proposes that deposits in the chamber leads to increased compression (!!)
which in turn leads to an increased octane requirement (of the fuel) to be used.
My point is that burning oil doesn't lower the octane of the fuel being used, as is commonly repeated over the internet. Yes indeed the highest specific output engines, 2T and those powering F1 cars are designed to burn oil as fuel.
Latest research suggest low speed pre-ignition issue plaguing downsized DI & DI turbo cars, first thought related to carbonised coking (of the intake valve and chamber) deposits accumulated via PCV, is related to combustion of detergent oils though blow-by under certain temperatures and load conditions. Specifically the oil turns to an emulsion which when mixed with fuel under (DI) pressure ignites prematurely. This relatively rare and uncontrolled emulsion is neither oil or petrol rather a third hydrocarbon product from detergents in the oil.