In a certain context Jesus speaking to the religious leaders makes the following remark
“-and Scripture cannot be broken—” John 10:35
The NT has texts that are used either to support doctrine and theology by Jesus and NT authors or quoted directly, implicitly claiming authenticity and divine inspiration however they are non canonical sources, one example being Jude 14,15.
Clearer still, we have Scripture endorsing non canonical books for further reading such as the “Book of the Wars of the Lord”, “Book of Jasher”, “Book of Nathan the prophet”, Book of Gad the Seer”, to name a few.
In light of Jesus’ remark that Scripture cannot be broken as translated in English, λυθηναι in the Greek, which could be translated as Scripture cannot be “discarded” in the ultimate sense, is Jesus saying these books, that did not make it in the canon, are these books still considered Scripture therefore? And that they cannot be broken or discarded? In fact they ought to be read and studied? Or is this a stretch?
(Consider including in the answer the overarching reason for the choice of books in the canon, which may or may not have disqualified other Scriptures however they didn’t fit within the purpose for the selection of the canon).