As a spin-off from the discussion about dating the Buddha’s lifetime I’m offering the following topic…
One hint for locating the time of ETB would be looking for external references in the Tipitaka. I guess many things could be researched here, for example the names of kings etc. and there is probably research about it. I would like to focus on the Vedas…
Today we refer to four Vedas. In many places in the Suttas only three Vedas are referenced. The Milindapanha however (between 100 BCE and 200 CE) already mentions ‘our’ four Vedas by name (in 5.3.7). This is not so much the question about when the fourth Veda was composed but rather when people started to refer to the ‘four Vedas’
Early brahmanic sources referring to four Vedas could help establishing the minimum age for the Buddha’s lifetime. I don’t know if these sources exist, but I’m sure Indology had the question of the age of the Vedas before…
Here are Sutta sources which mention a number of (mostly three) Vedas:
tiṇṇaṃ vedānaṃ (as a genitive): MN 91, MN 92, MN 93, MN 95, MN 100, DN 3, DN 4, DN 5, AN 3.58, AN 3.59, AN 5.192, Snp 3.7, Snp 5.1 and the Culanidessa (https://suttacentral.net/pi/cnd7), plus about 12x in the Therāpadāna
tayo vedā: SN 35.132, Mil 2.1 (in the same chapter four Vedas - catubbedā - and later as mentioned the four Vedas by name - ?!, I can’t seem to find another reference to four Vedas)
tevijjā is mentioned often, but I don’t count it as it’s not a literal reference to the Vedas
SN 1.38 mentions 5 vedas (Pañcavedā) - a mistake? there is no other mention of five Vedas. There are only inconsistent references to a ‘fifth’ Veda: https://en.wikipedia.org/wiki/Fifth_Veda
The PTS dictionary says: “…Dpvs v.62, where the 3 Vedas are enumerated as iruveda yaju˚ and sāma˚”