With S&W, never say never. I've seen a lot of K22s, and all of the ones I've seen have that same 1 line. We can also say they're all 5 screw guns, but there might be an exception (probably not.) What we're talking about are the 150 guns made in 1946, and then the next 9850 guns made in 1947. Most of the 1948 guns also have that same info line, taking you up to about K70,000. Pretty solid evidence.
Where you start running into the Marcas Registradis crap is on export guns. You will also see the more modern stamp placed on some guns that were factory refinished. I had a beautiful Triple Lock with a 3 digit serial that had the 1950s vintage stamp. On the letter Roy stated that was one big reason they stopped refinishing old guns. People complained about the restamping.