Indo-Scythians
I haven't seen much discussion about this but I think some of them were L657. And they did leave quite a big footprint.
So, starting off:
https://www.yfull.com/tree/R-Z2124/
Notice that most of the South Asians east of the Indus (i.e, not Pashtun) are actually from way further in India, often South and Southwest India. There is one branch which is in Haryana/Rajasthan:
https://www.yfull.com/tree/R-FT78161/
Which is fascinating, but it splits off from a line that's also in South India.
Obviously this is because the Indo-Scythians set up kingdoms across the subcontinent, particularly in the southwest.
https://en.wikipedia.org/wiki/Indo-Scythian_Kingdom
https://en.wikipedia.org/wiki/Western_Satraps
The northern kingdom:
https://en.wikipedia.org/wiki/Northern_Satraps
But we don't see a lot of the northern lineages in consumer testing today, at least not as many as from the southwest. Which is perhaps not entirely surprising considering how successful those kingdoms were and the ensuing population boom.
It's interesting to note that even though we know when the Indo-Scythian kingdoms were established (well into the Iron Age), if you look at the branching points of their lines, some are branching early Iron Age or even late Bronze Age. These branches split up in Central Asia and then came grouped together into South Asia.
I'd wager that branching points with non-South Asians that are in the Iron Age are almost a dead giveaway, if the additional historical context is there, for Indo-Scythians. And you see plenty of these in R-L657 (often with Chinese/Kazakh/Kyrgyz/Tajik/etc). However, this is all dependent on how accurate the age estimation is.
From the limited results we have, it seems like an awful lot of the L657 lines are candidates for an Iron Age dispersal into South Asia. Curious as to others' thoughts?
Also, I believe I've found an Indo-Scythian branch here in J2b2-M241 (under M241>Z2432>Z2443>Y978):
https://www.yfull.com/tree/J-Y958/
There are three Iron Age Saka samples under this branch visible here:
https://discover.familytreedna.com/y-dna/J-Z8330/tree (This is J-Y978, J-Z8300 is J-Y958)
There is a Bronze Age BMAC from Turkmenistan (I7472), Iron Age Saka from Xinjiang (Caishichang 1-2, who was found next to an R-L657 grave!), and two more Iron Age Sakas from Turkmenistan (I25913, I5091).
The branch the two Turkmenistan Sakas come off of, J-FTG27149, has a cluster found in Portuguese Azores (so, likely via Goa). There's a bunch of other Goans in other branches here as well, more than we've found in R-Z2124 to date actually. That alone (multiple Iron Age Saka genomes plus the closest South Asian relatives being upper class/mercantile Goans) is a smoking gun. And that too without the more recent Iron Age TMRCA branching points
The next major split (J-Z8316) has Chinese, Tajik, and Arab users. The two Pakistani Punjabi close relatives are Awan if anyone's curious. The subclade J-FT19403 is found in a Pakistani Pashtun (who claims a recent Afghan paternal ancestor) and then Arabs.
The other Indian samples prefixed with ERR are Vellalar. There's 3 of them.
So in this one line, it looks like a connection to both the Western and Northern Satraps. I don't think the Pashtun/Arab line was a migrant back out of India, though it's possible. But they neatly split up at 3100ybp into South Indian, Punjabi, and Afghan/Arab branches.
So this was a local South Central Asian BMAC lineage that got absorbed by Sakas and then spread around a bit.
But looking at this is a clue for what to look out for in other branches. And I'm seeing R-L657 branches with TMRCA of as recent as 2800ybp between Chinese, South Asians and Arabs. They were there the entire time right under our noses, but everyone just assumed they were completely South Asian from the Bronze Age.
I'm in J-M241 so I've been following the tree's growth for years and I remember in the early days of the YFull tree over 10 years ago, there was only J-Y960 where this branch is now and everyone thought it was a neolithic expansion into India.
EDIT:
Here's an L657 example, a candidate based on age estimates:
https://www.yfull.com/tree/R-Y16494/
https://discover.familytreedna.com/y-dna/R-Y16494/story
https://www.theytree.com/tree/R-Y16494
In this case, FTDNA's TMRCA estimate is closer to YFull's and both are more recent than 1000 BCE. You can also view Group Time Tree from the R1a group projects.