the documentation notes currently say that the M592 corrections aren't applied to extruder advance and retract moves.
Yes, but i'm not saying they are either.
It's that the corrections are often very violent (on long bowdens) by necessity - for example during infills.
So speeds like the ones tested are very much in the domain of normal printing - even though you won't get speeds like that on average, or on most of the print, you will in peaks, due to forementioned corrections.
So, i'm testing extreme speeds on an uncoupled extruder, doing extruder only moves, where, yes, linear advance is not applied, but it doesn't have to be - as i'm commanding extrusion rates that are (hopefully) similar to what you'd see during violent retractions OR violent linear correction moves.
Hope that makes it clearer.