The 6" K22 began shipping again in 1947 after WW2 ended in 1945.
The post war versions were very different than the pre war versions and had a new raised narrow rib barrel, the K32 and K38 had the same narrow rib profile until abt 1950 when they widened the barrel ribs as an attempt to weight match the three, ( think bigger .38 holes in the cylinder = lighter gun, widening the rib added weight).
Around 1948 a 4" version is tested and becomes regular production by 1950 but with the narrow rib because they wanted to keep it lighter.
The narrow rib 6" guns fade out of production by 1955, from that point the 6" K target guns used different style barrel and frames, that continued until the end of the dash 4 revision.
The 18 line was discontinued and the 17-5 was instead offered in 3 barrel lengths with a new wide rib heavier barrel basicly matching the lines of the old Model 14.
That's where the 17-5 you are looking at fits in.
The 17-6 used that same barrel for a short time until it was changed to the full underlug barrel during 17-6 production.
Here's where it gets weird, the Model 15-5 continues as it's own line but now with the old wide rib barrel of the Model 14 in 4" and 6" ( maybe an 8 3/8" ? Never seen one)
And the Model 14 line gets a full underlug barrel in the various lengths...weird?
There was a recent thread showing a rare varient called the 617 Ashand gun which is a stainless copy of the 17-5 you are looking at.
As for it being "Special" ? I think so because it's unique and didn't have a very long production run so to a K22 collector it's different and needs to be acquired to fill the slot, in reality it won't do anything your old 5 screw won't.
Post some pics if u get it,
If you are interested in the Model 18 evolution here's a link to a pictorial essay outlining it's evolution. ( scroll down to post #25 to begin)
Some Combat Masterpiece eye candy