There is a lesser-known Latin term for the matter you ask about, namely, Tota Scriptura (“Scripture wholly” or “every part of Scripture”). This is a way of saying that the entire Bible is equally inspired by God. Tota Scriptura is also called the plenary inspiration of Scripture.
This means that the issue is not about when scripture was written, nor when it was agreed by Jewish and/or Christians leaders to be inspired of God in any official canon. The inspiration bit comes from "God-breathed" moving of his words into action. In the case of the Bible, those words had to be uttered first, either by God, or by his prophets, or even by the enemies of God who were speaking without knowing that God was moving them to so speak.
Some God-inspired prophets thus wrote how God directed them to write:
"So shall my word be that goeth forth out of my mouth: it shall not
return unto me void, but it shall accomplish that which I please, and
it shall prosper [in the thing] whereto I sent it" Isaiah 55:11.
"For ever, O Lord, thy word is settled in heaven" Psalm 119:89.
"For thou hast magnified thy word above all thy name" Psalm 138:2.
That is why God is also reported in the Bible as speaking approvingly of people "who tremble at my word" (Isaiah 66:2). Just as powerfully, the prophet Malachi wrote:
"Then they that feared the Lord spake often one to another: and the
Lord hearkened, and heard it, and a book of remembrance was written
before him for them that feared the Lord, and that thought upon his
name. And they shall be mine, saith the Lord of hosts, in that day
when I make up my jewels; and I will spare them, as a man spareth his
own son that serveth him... But unto you that fear my name shall the
Sun of righteousness arise with healing in his wings" (Malachi
That ending to the last book in the Hebrew scriptures has parallels with the ending of the last book of the Christian Greek scriptures, where symbolic 'books' are opened in heaven, to judge the resurrected dead from, and then there is the book of Life, where the names of those who will live forever in God's holy presence are recorded. We do not have access to such holy, scriptural, God-breathed books here on earth. But we do have the record of God's dealings with humankind in God-breathed (inspired) texts dating from Moses to the apostle John.
This means that the cannonisation of any part of the Bible has no bearing on the doctrine of Tota Scriptura, for the scriptures in question are the words of God he first utters, or causes to be uttered, only after which are some of them written down in books that we can read, on earth. There are other 'books' in heaven that we cannot read, but we will get to know their contents on the Day of Judgment, and discover the lists of names God recorded as of those people who tremble at his word now.
In answer to your question, then, yes, the scriptures in question are certainly "referring to the Jewish Pentateuch or the OT". But unless a Christian thinks God stopped speaking 400 years before Jesus was born, never to speak again to the world in general, or to his people in particular, then all the writings about Christ and about the first century church are included in the totality of God-breathed scripture. To claim that only the OT scriptures can legitimately be called scripture, would mean claiming God stopped his revelation 400 years before the OT prophecies about Christ began to be fulfilled!
As it is, using nothing but the OT scriptures, it is still perfectly possible to show that the fulfilling of them is equally God-inspired, and that the Christian Greek scriptures are perfectly in accord with the Hebrew scriptures. I have quoted nothing but Hebrew scriptures in my answer.
See https://www.gotquestions.org/tota-scriptura.html and the related links on that page.