It is hazardous to put too much faith in the ranges given in the Standard Catalog. I've been looking at and tracking the M&P for years. I have yet to find a C prefix unit as high as C223xxx that shipped as early as 1951.
Examples:
C208861 shipped in July, 1952
C218272 shipped in September, 1952
C226955 shipped in December, 1952
C232901, C236440 and C237760 all shipped in June, 1953
What we do know is that, broadly speaking, numbers C1 through about C44,000 left the factory in 1948. C1 was actually assembled on March 22, 1948, and shipped to a distributor in Minneapolis, together with 99 other M&P units. 50 of them had 5" barrels and 50 had 6" barrels.
