1 Corinthians was written in 55 A.D. We can date when Paul was in Corinth by the inscription in Delphi of Greece. Gallio was the procouncil in Corinth. We can trace all of Paul's writings to that archaeological discovery. Look at 27:00 by Frank Turek.

The creed in 1 Cor. 15 is pre-40 AD. Nothing in antiquity has reference points this close to their events, thus, holding to the higest of standards for ancient literature. If you look in John or Acts there are details recorded which only John or Luke could have known as eyewitnesses or had known the eyewitnesses. Church fathers are quoting from the NT in the 1st century. There's also a commentary written in the first century about what went down. In fact, someone noted you can quote the entire NT except for 11 verses from the earliest church fathers.