This thread is about Indo-European score not Yamnaya score.
Yamnaya did not appear ex nihilo and do descend from earlier pre-proto-indo-european speaking cultures associated with populations rich in EHG-SHG-WHG that gradually supplanted supposedly Basque-like languages speaking Neolithic Europeans.
The keyword is that the genetic distance between EHG-SHG-WHG and CHG are very small and that means that they all descend from the same common ancient preproto-indoeuropean speaking population; rich in R1a and R1b Y-DNA.