It's not simple, that's for sure

An author may “quote” another text inexactly. An author may work from memory and simply record a slightly different version of the text, or an author may also deliberately alter the quotation to fit the context or to make a different point. One should attempt to make a decision regarding these alternatives since the presupposition of an intentional change or an oversight can directly impact how one interprets the function of the quotation.—James D. Nogalski, “Intertextuality and the Twelve,” in Forming Prophetic Literature: Essays on Isaiah and the Twelve in Honor of John D. W. Watts, ed. John W. Watts and Paul R. House, JSOTSup 235 (Sheffield: Sheffield Academic, 1996), 104