Coptic scribes had an awareness that their texts were of a different type than those used within the Imperial Byzantine tradition.
"Corrections indeed occur in all [Bohairic manuscripts], yet frequent notes in several state that the corrections are Greek and not Coptic, implying as plainly as possible that the Jacobite Copts jealously preserved a tradition as to the correct readings of their version against Melchite, i.e. Contantinopolitan readings or innovations" (George W. Horner, [ed.], The Coptic Version of the New Testament in the Northern Dialect, vol. 1 [London: Clarendon Press, 1898], ix–x).
Do we have any parallel statements in the Syriac or Latin traditions? Scholars knew that Erasmus' Textus Receptus deviated from the Vulgate. Do we have any formal statements accusing the Greek (Byzantine) tradition of corruption during or before Erasmus' life?