As we read what Ron Cameron writes on the Gospel of Thomas, we need to remain cognizant that there are other works that are ascribed to Thomas. Some of these works are dated to the third century, while the Gospel of Thomas is said (depending on who does the saying) either in middle of the first century (some few years after the death of Jesus) on the first part of the 2nd century. Cameron says:
The fact that Judas “the Twin” was the apostolic figure particularly revered in Syriac-speaking churches is important evidence for the date and place of composition of the text. For as Koester (in Layton 1989: 39) has shown, Gos. Thom.’s identification of this author as Jesus’ brother Judas does not presuppose a knowledge of the NT, but “rests upon an independent tradition.”
In addition, the peculiar, redundant name Didymus Judas Thomas seems to be attested only in the East, where the shadowy disciple named Thomas (Mark 3:18 par.; John 14:5) or Thomas Didymus (John 11:16; 20:24; 21:2) was identified with Judas in the Syriac NT and called Judas Thomas (John 14:22).
The occurrence of variants of this distinctive name in the Acts of Thomas is especially striking, not only because the latter evidently shows acquaintance with Gos. Thom. 2, 13, 22, and 52, but also because it is widely held that the Acts of Thomas was composed in Syriac in the early 3d century. Other documents that invoke the authority of Judas Thomas by name are also of Syriac origin, such as the Teaching of Addai,the Abgar legend (Eus. Histl. Eccl. 1.13.1-22), and the Book of Thomas the Contender (NHC II, 7).