The earliest full copy of the psalms dates from the 4th century.
it is in Coptic. Not Hebrew. .
The Interpretation espoused by Theodore of Mopsuestia also dates from the 4th century AD.
While Mopsuestria was in a different area; not Coptic, nevertheless, considering this was a period of time where establishing defacto standards for what belongs and what doesn’t belong, it’s likely that Theodore’s text in his language was functionally identical to the earliest surviving Psalms.
This to me, would mean if the earliest physical source material is dated in the same era as the first interpreter of the Psalm that I can find…
…his interpretation would be likely the closest to proper.
Now, this can be wrong. I’m searching for earliest archeological evidence of Psalm 137. Maybe something in Greek. Maybe Latin. Maybe Hebrew.
So far, can’t.
So far, it’s Coptic.
Now the Septuagint; the first complete Septuagint and New Testament is from 450 AD
So even if you don’t like the Coptic from the 4th Century as the complete Psalms, you can have the whole thing about 70 years later.
Still a lot closer than … oh.. .let’s see… when we are today… interpreting it from our perspective in the 21st century.. rather than theirs in the 4th and 5th centuries.
21 – 5 = 16 centuries.
21 – 4 = 17 centuries.
Whose interpretation is closer to potentially being accurate?