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You would never get knocking from too much timing advance when you take your foot off the gas. However many people run way too much advance when driving. I run mine 28-30 degrees with the lever all the way down and that is plenty with todays fuels.
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Per my go-to on these things (Vince Falter at fordgarage.com)
http://www.fordgarage.com/pages/bdistributoradvance.htm
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The measurements above show that the initial static Model B ignition timing point of 19 crankshaft degrees BTDC plus a maximum mechanical centrifugal advance of 17 degrees equals a theoretical geometric maximum total advance of 36 crankshaft degrees. The slots in the centrifugal flyweights limit their travel and the timing advance.
Compare this to a Model A distributor which has an initial timing point at 0 crankshaft degrees TDC plus an actual manual maximum advance of 40 crankshaft degrees. The the breaker plate arm notch in the bakelite distributor body limits the travel of the plate and the timing advance.
The Model A ignition uses a zero crankshaft degree (TDC) initial timing point so that the engine can be easily started by hand crank, however it should never be run under load in this "retarded" position. The advance lever should always be advanced 1/3 to 1/2 travel (13 to 20 crankshaft degrees BTDC) on the steering column quadrant after starting the engine, and should generally not be run more than 3/4 advanced on the column under any normal circumstances.
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Bolded mine
Fuels today are more "knock resistant" (higher octane) allowing one a greater advance without knock, but there is a "mechanics" to advance too which is irrespective of the fuel. One wants the fuel combustion to occur in a range where the engine can best use it. Just because it doesn't knock the head off doesn't mean you CAN do it - or want to.
Joe K