The accepted ancient Hebrew diachronic paradigm and the standard linguistic approach for the periodisation of biblical texts are today heavily criticised, the criticism most recently centring on the textual situation of the sources. Critics argue that the high degree of textual instability and linguistic fluidity characterising the extant witnesses preclude any reliable tracing of the history of the language and make even the most approximative attempts at linguistic dating impossible. However, much of this textual argument is abstract, since the effect of secondary intervention on the stability of diachronically significant features has been studied in detail in the case of only a few texts, the investigations reaching conflicting conclusions. After a brief survey of foregoing investigations, the present study compares Pentateuchal material from the MT and Qumran, concluding that (a) preservation of diachronically meaningful detail is still very much the norm, and (b) differences between editions of the Torah often indicate the linguistic conservatism of one edition, here the MT, as opposed to linguistic development of the other, here the Qumran material.