I should amend my statement to: “you cannot use words or a language to [accurately] date a document.” Here’s a few problems one needs to look out for in connection with language use in a MS. Few would argue against the fact that many editors were involved with the production of the finished product of the book of Daniel. The Jewish Talmud implies that "men of the Great Synagogue" edited parts of Daniel (also cf. MT with Greek versions). If you do not have an earlier MSS to compare it with, you’ve got a problem with those editorial changes and insertions.
E.g., the complete Isaiah scroll (1QIsa a) from Qumran, is viewed by scholars as a vulgar modernization of the Proto-Masoretic Text. The scribe of 1QIsa a was not interested in a faithful reproduction of the Proto-Masoretic Text. He tried to adapt the material in such a way that the common person would understand. Unfortunately the average person could barely read the Proto-Masoretic Text, let alone interpret it.
In this regard Encyclopaedia Judaica says: “As has been noted above, the average reader was scarcely able to understand the MT properly, and often unable to read it correctly. Therefore, copyists often substituted contemporaneous forms for the original ones even in the case of proper nouns. For example, the form ys`yh, `thyh, representing the type that became common mainly after 586 B.C.E. (the destruction of the First Temple), is used instead of the original ys`yhw, `thyhw which represents the dominant type during the previous period. w'th khl 'lh ydhy `sthh wyhyw khl 'lh(“All these (things) my hand has made”) of Is. 66:2 became w'th khl 'lh ydhy `sthh whyw khl 'lh(“and so all these things came to be (mine)”), etc.
More examples can be found in the efforts of the LXX-translators to make the Old Testament intelligible to their compatriots. This led them to use terms native to their Egyptian and Alexandrian environment, words that had no equivalents in Hebrew. E.g.,, ngshym (“slave drivers”) of Ex. 5:6, 10, 13 became ergodiouktai (“overseers, foremen”), a term familiar to us from the papyri of Hellenistic Egypt.
For the particularly difficult list of fashion novelties in Is. 31:18 - 24, which were strange to the translator, he simply supplied a list of comparable items from his own age and environment. “We cannot call his work here ‘translation’; most of the expressions are substitutes rather than equivalents. Thus the Greek translation often refers to completely different objects, and is useless for determining the meaning of the Hebrew word.”
“Finally we should note the attempt to make ancient words relevant to contemporary circumstances in Egyptian life. In Deut. 23:18 we read: “There shall be no cult prostitute (qdhsh, Greek pornei) of the daughters of Israel, neither shall there be a cult prostitute (qdhs, Greek porneuoun) of the sons of Israel”. The choice of terms pornei and porneuoun for qdhs instead of hierodoulos already alters the meaning of the passage. Nevertheless, even more significant is the addition: ouk estai telesphoros apo thugateroun Israeil, kai ouk estai teliskomenos apo uioun Israel. The term’s telesphoros and teliskomenos refer to the participation in the Mysteries. As cultic prostitution was a temptation in Hellenistic Egypt. The Egyptian translators felt as justified as the Targumists in linking the text to their time.” [i]
[i] E. Würthwein, The Text Of The Old Testament An Introduction to the Biblia Hebraica, pp. 67, 77.