The notion that the pronunciation of the tetragrammaton was lost is fiction

Popular wisdom has it that the pronunciation of the Name was "lost," but that it was pointed with the vowels for Adonay.  The transliteration of the consonants YHWH + the vowels for Adonay = Jehovah.

Well....not quite.

Jehovah is the product of the combination of YHWH + the vowels for Adonay.  That part is correct.  The incorrect part is that the text was pointed with the vowels for "adonay."

Why is this incorrect?  because texts of the time were without spacing between words and lacked nekudot (vowel points).

So how do we get "Adonay" as the name substituted for the Name that cannot be pronounced?

The LXX.

We find in the LXX that the Name is not transliterated from Hebrew into Greek (an impossibility because Greek lacks a consonantal sound approximating the soft "h" of ה .  So there was no means by which the Name could be represented as its full complicated verb.  The Name that was substituted in the text was one that would be recognized by all, Greek-speaking/literate Judeans and Greeks/Romans, as a Name to be respected:  κυριος , "lord."