A variant of the K-Ar method gives better data by making the overall measurement process simpler.
Next, the mineral sample is heated to melting in a vacuum furnace, driving out all the gas.
The Ar-Ar method is considered superior, but some of its problems are avoided in the older K-Ar method.
Also, the cheaper K-Ar method can be used for screening or reconnaissance purposes, saving Ar-Ar for the most demanding or interesting problems.
These dating methods have been under constant improvement for more than 50 years.
The learning curve has been long and is far from over today.