H. Houghton has reported in "Recent Developments in NT TC (2011, Early Christianity 2.2, p. 245-268:
"...There have also been developments in the dating of certain manuscripts. The Freer Gospels (032, W), famous for their unique text in the Longer Ending of Mark, were initially assigned to the fourth or fifth century. However, following the redating of the manuscripts used for the original comparison and the subsequent discovery of similar material, including the Cologne Mani Codex, Schmid has suggested that it may have been copied at least a century later.  Parker and Birdsall's consideration of the palaeography and catena of Codex Zacynthius (040, Ξ) prompt them to propose a date of around 700 for the majuscule underwriting, rather than Hatch's suggestion of the sixth century.  The date of the earliest surviving fragment of the New Testament, P52, has also been the subject of a recent review by Nongbri.  This cautions against the uncritical adoption of the earliest suggested date of 125 CE and demonstrates that a date in the late second or early third centuries remains palaeographically possible. As more and more comparative material becomes available online, it will not be surprising if the dating of other manuscripts is reassessed. ...
29. Ulrich Schmid, "Reassessing the Palaeography and Codicology of the Freer Gospel Manuscript," in The Freer Biblical Manuscripts: Fresh Studies of an American Treasure Trove ed. Larry W. Hurtado (SBLTCS 6. Atlanta GA: SBL, 2006), 227–49.
30. D.C. Parker and J. Neville Birdsall, "The Date of Codex Zacynthius (Ξ): A New Proposal," JTS 55.1 (2004): 117–31 (reprinted in Parker, Manuscripts, Texts, Theology, 113–20).
31. Brent Nongbri, "The Use and Abuse of P52: Papyrological Pitfalls in the Dating of the Fourth Gospel," HTR 98.1 (2005): 23–48.
It seems what has long been suspected by outsiders is turning out to have some substance and basis, namely that manuscripts generally have been dated too early, and more revisions are in the works, either by their over-enthusiastic discoverers, or else apologists.