I would also be interested on your comments on what the great Leolaia had to say on this subject a few years ago, here is her Post :
"The evidence is quite clear
that Adonai was a frequent reading substitute for the Tetragrammaton by the
first century BC.
We find it replacing YHWH in quotations from
the OT in the Dead Sea Scrolls, and as a favoured divine epithet in some of the
Most telling is the Great Isaiah Scroll in the
Dead Sea Scrolls, where the scribe sometimes accidentally writes Adonai instead
of YHWH and sometimes vice versa. Clearly the scribe mentally pronounced
YHWH as "Adonai". This reflects the ketib-qere principle where
one thing is written but it is read a different way.
Adonai wasn't the first
substitution. Earlier on, Elohim was a common substitute for YHWH, as one
can see in the Elohistic Psalter (Psalm
42-83), where Elohim replaces YHWH in the same passages
elsewhere in the Psalter. This Elohistic redaction possibly dates to
around the same time when Ecclesiastes was written (fourth or
third century BC), where Elohim is the preferred DN.
We can also see that Paul, in
reading the OT pronounced YHWH as kurios "Lord" (cf. Romans 10:9-13 citing Joel 2:32, 14:6-11citing Isaiah 45:23).
This brings up a point that is usually ignored
in these discussions, which tend to focus too much on the graphemic
representation of the Tetragrammaton in the LXX.
It isn't simply a
matter of YHWH appearing in the LXX, and therefore it was "used", but
rather how those characters were pronounced (remember, biblical texts were
usually read aloud). Regardless of whether YHWH was written in Hebrew
characters in Paul's Bible or replaced by kurios, the name was
pronounced kurios by Paul. And the tendency
to represent the Tetragrammaton in archaic (and often incomprehensible) Paleo-Hebrew
characters in the midst of Greek lettering is a clue that probably it wasn't
read letter for letter but rather recognized in toto as the ineffable name and
handled however that name was handled by readers."