A new paper for David Anthony mentions something which I had missed:
The currently oldest sample with Anatolian Farmer ancestry in the steppes in an individual at Aleksandriya, a Sredni Stog cemetery on the Donets in eastern Ukraine. Sredni Stog has often been discussed as a possible Yamnaya ancestor in Ukraine (Anthony 2007: 239-254). The single published grave is dated about 4000 BC (4045–3974 calBC/ 5215±20 BP/ PSUAMS-2832) and shows 20% Anatolian Farmer ancestry and 80% Khvalynsk-type steppe ancestry (CHG&EHG). His Y-chromosome haplogroup was R1a-Z93, similar to the later Sintashta culture and to South Asian Indo-Aryans, and he is the earliest known sample to show the genetic adaptation to lactase persistence (I3910-T).
The sample goes back to 2017 paper.
As you know the R1a1a-Z93 is the sub-branch of R1a1a that is common outside Europe (Central Asia & South Asia). A previous sample was dated to 3,800 years ago from a Sbruna sample, and it is rather common on the Central Asian steppe of the period as evidenced by ancient DNA. The details of its intrusion (or lack thereof as some might say) into South Asia have not been fully elucidated by ancient DNA, but they likely will be soon.
Additionally, the I3910-T mutation is known to share identity-by-descent between people in South Asia and in Europe. That is, the mutation in both populations is due to a common ancestor.