That's for sure. I have seen exactly 4, 2"-barrel, S prefix revolvers for sale in the past 2 years. 2 of those were real junkers.
My crummy database is not nearly as complete as yours, but I offer some additional 6" data points of guns I have observed. I do not own any of these guns.
S814xxx, Blue, 6", wrong grips.
S819037, Nickel, 6", refinished (*), pre war service grips.
S819968, Blue, 6", pre war magnas, customized like a pre war M&P target?
S820116, Blue, 6", Maroon box, pre war magna grips w/machined circles. WOW!!! WOW-WOW-WOW!!!
S820222, Blue, 6"
S820280, Blue, 6", No "S" on barrel flat or cylinder, no orig grip.
S871603, Blue, 6", Barrel nut ejector, wrong grips.
S871757, Blue, 6", Barrel nut ejector.
S874756, 6", Nickel, knurled ejector rod, wrong grips.
S908778, Blue, 6", nice,
S909586, Blue, 6".
S91124x, Blue, 6", knurled ejector rod.
S924601, Blue, 6", Knurled, non matching later DC magnas.
S927090, Blue, 6", fake stag grips.
S928006, Blue, 6", Nice gun.
S928588, Blue, 6"
S928709, Blue, 6"
S942931, Refinished nickel, 6".
S944885, Blue, 6", Kings Super Target conversion w/Sanderson stocks. ($4000!)
S945000, Blue, 6".
S986322, Nickel, 6", 4 line address, short throw(fish hook) hammer.
In support of this statement, I supply the following information drawn from the approximately 15,000 units in my early postwar M&P database:
Various barrel lengths and grip configuration from most common to least common:
4" square butt
5" square butt
2" square butt
6" square butt
2" round butt