So what's the date of the earliest surviving manuscript of the canonical Gospels?
"So what's the date of the earliest surviving manuscript of the canonical Gospels?"
Most believe he oldest "new testament" writings are those by Peter (his letters), which are obvious near-contemporaneous writings, given Peter's well-documented (by Christian and non-Christian sources) execution by Rome not too long after Jesus.
Peter's letters clearly state, or require as knowledge to make sense, many or most of the accounts found in the gospel --- most notably the death and resurrection of Jesus.
In sum, my somewhat non-answer to your question is the gospels-written-long-after dispute is a bit of a red herring.