Genetic and archaeological continuity from Khvalynsk to Yamnaya

Over a year ago, using the D-stats/nMonte method of mixture modeling (see here), I noticed that Yamnaya did not appear to be simply a two-way mixture between Eastern European and Caucasus Hunter-Gatherers (EHG and CHG, respectively), but the result of a much more complex process:

Using the most plausible reference samples currently available - almost all of them older than Yamnaya, and thus