4QNum-b has expansions matching the Samaritan Pentateuch, so it isn’t quite true that the copies match the later text.

A fair refinement. 4QNum-b is a mixed text that sometimes agrees with the Samaritan tradition and sometimes with the Septuagint against the Masoretic. That is a real finding, and stating it plainly strengthens the case rather than weakening it. The narrative and legal content of Numbers is stable across all of them; the differences are the kind textual critics use to reconstruct the earliest form of the text, which is what a recoverable tradition looks like.