I track the single-line K-38s, and the highest serial number known to me is K25257. The lowest serial number I know on a four-line K-38 is K35184. Among dated guns, no single-line K-38 known to me shipped after May 1948. The earliest shipping date I have for a four-line gun is July 1948. The order to go to the four-line address block was issued in April 1948. The K-38 was first shipped in commercial quantities in February 1948.
I have 36 single-line K-38s on my list, three of which have not been observed but are known from factory records. Serial number clusters (approximate ranges, so don't take these as hard and fast numbers) are K4500-K4900 and K22700-K25300.
I estimate that of all Masterpiece production numbered below K30000, about 90 percent are K-22s and 10 percent are K-38s. It's possible for the K-38 segment to be smaller than that, but it is almost impossible for it to be larger based on the serial range constraints. There will be a few prototype and salesman sample K-32s as well, but not enough to matter.