It doesn't need a dash, and the K is part of the serial number. Just how they did it back then.
Also, don't feel too secure in it being a 1947 production gun. The tables are pretty loose as to the dates. None of us know with any degree of certainty when guns were shipped to the customer/sporting goods store. That is the only date that is really obtainable. You can write the company historian and pay him $50 and he'll tell you where it went originally, and when.
I'm going to make a guess here, and since nobody really knows or can prove or disprove it, we can only use logic. I'm going to suggest that the number Roy originally furnished in one of his books relates more to when a gun was in production than when it shipped. Many of us have lettered our K22s (and other K series guns) only to discover the rules aren't set in stone. Guns we've assumed to have shipped in late 1946 actually went out in 1947 (examples of this are my K22s #K155 and #K166.) According to all the tables, they're 1946 guns, but they both letter as 1947. Similarly, some of the guns with serials in the K12000 to K18000s we think were 1947 guns were really 1948 shipments.
We also know that during the early postwar years returning GIs were clamoring for guns, and K22s were a really hot seller (Skeeter Skeltons writings as evidence.) Since S&W was in some financial straights at that time, its also pretty fair to assume they were shipping every completed gun as soon as they could.
S&W didn't produce or finish guns in numeric order. We all just assume they did, but Roy keeps beating on us telling us they didn't.