Close as I come is 594451 (shipped March 8, 1929)------and 640816 (shipped February 8, 1932)-----and these are both targets (spelled slow movers)----so their shipping dates could be more out of whack than usual. And having said that, standard M&P's were not slow movers---and shipped pretty much as fast as they could make them (comparatively speaking).
And as far as being rational goes, one need only harken back to the Golden Rule------"Them what gots the gold makes the rules!". It's your gun---what you say is so. And when something is so, it doesn't make any difference if it's right/wrong/rational/irrational---or cream cheese----it is SO!!
Ralph Tremaine
Besides that, rational has nothing to do with this business! I was putting 640816's letter away, and noticed the rest of the paperwork----this being from the guy I bought the gun from. It says (in part): "This gun is 24 numbers away, and identical configuration to the one that McGivern set the record with in 1933." That made it rational for him to want half again as much as the gun was worth at the time. My options were to pay the price or pound sand down a rat hole. It was a flat mint gun. I deemed it to be rational to pay the premium price. It seemed like a good idea at the time----which was fifteen years ago. Right now, I don't recall if his claim was/is correct or not, but I'm glad I have the gun----never mind if it's kissin' kin to McGivern's or not!