There has been a lot of argument that the gospels were written much earlier. I tend to believe this. The various arguments I’ve read make a lot of sense to me, and I know liberal theologians love to date things later to help them explain away some of the power of the predictions. Earlier dating also explains the meaning of certain verses better.
For instance, Acts is considered a continuation of Luke, and Paul was still alive at the end of Acts, and we know he died about the year 64. So Luke must be earlier than that.
I'm wondering if there are liturgical fragments (e.g. hymns) that date pretty early. Oral history sometimes comes down as songs, because verse is far easier to memorize than prose text. I think some of the Epistles of Paul quote hymns.