What on earth are you talking about? I have read numerous books directly on GThomas and a host of scholarly journal articles. Not to mention many scholarly works on the historical Jesus as well where authors have to list and defend their source presuppositions. The vast majority date GThomas from 50-140.
From Peter Kirby on Early Christian writings:
The Gospel of Thomas is extant in three Greek fragments and one Coptic manuscript. The Greek fragments are P. Oxy. 654, which corresponds to the prologue and sayings 1-7 of the Gospel of Thomas; P. Oxy. 1, which correponds to the Gospel of Thomas 26-30, 77.2, 31-33; and P. Oxy. 655, which corresponds to the Gospel of Thomas 24 and 36-39. P. Oxy 1 is dated shortly after 200 CE for paleographical reasons, and the other two Greek fragments are estimated to have been written in the mid third century. The Coptic text was written shortly before the year 350 CE.
A very small number of scholars date it to 250CE. But the vast majority fit in the 50-140 range. He also have potential references by Origin and Hippolytus ca 225.
Obviously Thomas exists before we find partial Greek manuscripts of it it’s sayings. But it was a sayings Gospel and easy to alter and expand so it may have existed in multiple forms so when we date it we have to be conscious of what we are actually dating.
Patterson argued for 70-80 dating:
“While the cumulative nature of the sayings collection understandably makes the Gospel of Thomas difficult to date with precision, several factors weigh in favor of a date well before the end of the first century: the way in which Thomas appeals to the authority of particular prominent figures (Thomas, James) against the competing claims of others (Peter, Matthew); in genre, the sayings collection, which seems to have declined in importance after the emergence of the more biographical and dialogical forms near the end of the first century; and its primitive christology, which seems to presuppose a theological climate even more primitive than the later stages of the synoptic sayings gospel, Q. Together these factors suggest a date for Thomas in the vicinity of 70-80 C.E. As for its provenance, while it is possible, even likely, that an early version of this collection associated with James circulated in the environs of Jerusalem, the Gospel of Thomas in more or less its present state comes from eastern Syria, where the popularity of the apostle Thomas (Judas Didymos Thomas) is well attested.”
I’m not sure what conservative propaganda you have been reading but this is the standard dating range for GThomas which does not fit into the full pattern of second century gnostic texts.
Vinnie