As @Wubster100 stated above, sometimes different letters indicate different features or specs, also like different spring or shock rates. However, for the part numbers you listed, the are superceding numbers with the K version being the latest.
See this listing where it is clearly stating that the K version replaces the older ones. If you enter any of the older numbers it will automatically take offer you the K version.
So all will work, what changed between versions will probably remain a mystery to customers. Generally the latest is the best.