Spoken by the prophets? Yes, but where?

[dak]

Without pointing both netzer and natzar are written with the same Hebrew letters, נצר, (and there was no Hebrew pointed text in the first century). It is curious but true that there are certain forms of natzar that give us very close approximations of both city or town names found in the NT writings, but that is only because natzar is a verb, (verb conjugations come into play), while netzer is a noun. More specifically natzar, to watch, guard, keep, etc., has a form נצורי, which is Natzurei or Natzorei, (Nazoraios, Mat 2:23, but not actually related to the city or town called Nazareth/Nazarah). The Matthew passage does not use Nazarene but rather says, ναζωραιος κληθησεται, "he shall be called a Nazoraios". This form generally means preserve(d) and is seemingly employed in the sense of resurrection in the following passage, which plainly tells us that the Meshiah would be a preserved one, preserved by the Father Himself, (v.8).

Isaiah 49:5-9 KJV
5 And now, saith the LORD that formed me from the womb to be his servant, to bring Jacob again to him, Though Israel be not gathered, yet shall I be glorious in the eyes of the LORD, and my God shall be my strength.
6 And he said, It is a light thing that thou shouldest be my servant to raise up the tribes of Jacob, and to restore the preserved [נצורי, natzorei] of Israel: I will also give thee for a light to the Gentiles, that thou mayest be my salvation unto the end of the earth.
7 Thus saith the LORD, the Redeemer of Israel, and his Holy One, to him whom man despiseth, to him whom the nation abhorreth, to a servant of rulers, Kings shall see and arise, princes also shall worship, because of the LORD that is faithful, and the Holy One of Israel, and he shall choose thee.
8 Thus saith the LORD, In an acceptable time have I heard thee, and in a day of salvation have I helped thee: and I will preserve thee, and give thee for a covenant of the people, to establish the earth, to cause to inherit the desolate heritages;
9 That thou mayest say to the prisoners, Go forth; to them that are in darkness, Shew yourselves. They shall feed in the ways, and their pastures shall be in all high places.

The Natzorei of Yisrael were apparently preserved in Abraham's Bosom until Mat 27:51-53.

 

[Wick Stick]

Would the hypothesized lost books unknown to us have been widely known to Matthew’s audience?

Possibly, but the answer to that isn't important.

A major purpose for many of the 1st-century writings was to pass along the older words of the prophets. This phenomenon is so prevalent amongst the early church fathers that scholars have a name for it - the "golden apples in leaves of silver."

If they weren't familiar with it, then it remains that a purpose for Matthew's writing it may have been to hand something down to them that they didn't previously know.