Even within the period that runs from c. A.D. 100-300 it is possible for paleographers to be more specific on the relative date of the papyrus manuscripts of the New Testament. For about sixty years now a tiny papyrus fragment of the Gospel of John has been the oldest “manuscript” of the New Testament. This manuscript (P52) has generally been dated to ca. A.D. 125. This fact alone proved that the original Gospel of John was written earlier, viz. in the first century A.D., as had always been upheld by conservative scholars.

(Dating the Oldest New Testament Manuscripts by Peter van Minnen)

What emerges from this survey is nothing surprising to papyrologists: paleography is not the most effective method for dating texts, particularly those written in a literary hand. Roberts himself noted this point in his edition of P52. The real problem is the way scholars of the New Testament have used and abused papyrological evidence. I have not radically revised Roberts’s work. I have not provided any third-century documentary papyri that are absolute “dead ringers” for the handwriting of P52, and even had I done so, that would not force us to date P52 at some exact point in the third century. Paleographic evidence does not work that way. What I have done is to show that any serious consideration of the window of possible dates for P52 must include dates in the later second and early third centuries. Thus, P52 cannot be used as evidence to silence other debates about the existence (or non-existence) of the Gospel of John in the first half of the second century. Only a papyrus containing an explicit date or one found in a clear archaeological stratigraphic context could do the work scholars want P52 to do. As it stands now, the papyrological evidence should take a second place to other forms of evidence in addressing debates about the dating of the Fourth Gospel.

(“The Use and Abuse of P52: Papyrological Pitfalls in the Dating of the Fourth Gospel” by Brent Nongbri, Harvard Theological Review 98:23-52, 2005.)