Just a thought, but were the B-17s even modified? It is well known that incidents on (amongst others) this type led to the mentioned research and lever/knob shapes but it would not surprise me if the results only showed up on later types. By the time the defined shapes were becoming known, the B-17 must have been nearing the end of its service life (even though it soldiered on in many places) and a modification of this sort was perhaps deemed unnecessary?
I've looked at a photo of a restored (still flying) example and the only modification is a small cover or guard over the gear switch.