I got a webpage on the the topic (http://historical-jesus.info/ignatius.html) and concluded, among other things, the epistles were written much later that 110 CE, and certainly not by Ignatius of Antioch. BTW, I never used the Ignatian epistles as a terminus ante quem for the Gospel of Matthew, more so because datable other texts, combined with strong internal evidence, provide external evidence for a a terminus ante quem around 90/95 CE. See http://historical-jesus.info/gospels.htmlYou could get some better examples of the phenomenon you are trying to sketch. Perhaps the authenticity of Ignatius? It's been credibly assailed in every generation since the beginning of serious NT criticism (and even before then), yet still is used (for example) in a matter-of-fact way to set a terminus ante quem for the Gospel of Matthew in NT introductions. Essentially because of the defense of a few guys (especially Harnack and Lightfoot) in the early 20th century, who are now long dead.
Cordially. Bernard