The flare is a specified WS1 design feature. A WS1 barrel that has been cut (maybe b/c the very thin flare section got dinged up) might not have a flare.

WS2 has no flare, is similar to other Winchester chokes and tapers to the muzzle. I have never seen a factory Win choke with a significant flat section, as is common with aftermarket choke tubes from various makers.

Pre-64s in 28 and .410 stamped "skeet" do not have a constriction/flare like WS1.

Sam