Also, there are other factors to consider with the K target guns.
The following applies only to the K-38 Masterpiece, since the .38 Combat Masterpiece has a completely different sequence due to several factors, including when they were introduced and a fewer number of actual changes in the early days.
1. Narrow rib, tapered barrel examples are far less common than any of the straight barrel (Heavy Masterpiece) examples.
2. Examples with the barrel shaped extractor rod end are even more uncommon (actually pretty rare).
3. One-line address examples are more scarce than four line, but more common than those with the older style extractor rod (which are also one-liners).
4. Then you have screw count to consider: 5 screw from 1947 until 1956; then 4 screw from 1956 to 1958.
Note: the earliest model marked guns didn't ship until 1958.
So you see, BigBill, the matter is much more complicated than your question implies.
As an aside, I'll add two more points:
1. The .38 Combat Masterpiece is not a "K-38" despite the fact it is commonly referred to that way. We finally got that piece of misinformation more or less eliminated from the Standard Catalog with the 4th Edition (there are still remnants of it in the small print text).
2. Neither of the referenced guns stopped being called by name when the model numbers were
added by the management order of June, 1957. The .38 Combat Masterpiece became the
Model 15 .38 Combat Masterpiece; and the K-38 Masterpiece became the
Model 14 K-38 Masterpiece. And, as I mentioned above, neither of these newly numbered items became available for purchase until 1958.