I have a Kodak Reference Handbook from 1940 and it lists DK-60a, Replenisher DK-60aTR for deep tank hand processing and Replenisher DK-60aMR, for machine processing. The DK-60a and TR have formulas, the MR says available as a package, no formula given.
I also have Elementary Photographic Chemistry, published by Kodak in 1941 and it has the above, plus DK-60B. It's listed under "Formulas for Special Work", as a Kodalk Aero film developer. In a note it says for higher contrast use D-19 and for lower contrast use D-76.
So it looks like DK-60B was developed between 1940 and 41.