In Paul’s first letter to the Corinthians we have the earliest Christian record of the resurrection appearances and because it is the first it is the first in significance. It is not very good or useful to the historian. The first record that the historian would look at would be the gospel.
Mark was the first gospel and it says that Jesus' tomb was declared empty to women who came along on Sunday morning. Men in white announced the news. Their existence is very convincing when we have no record of Romans issuing a warrant for their arrest.
Mark gives no hint that there was any evidence that the men in white saying Jesus' body was gone were telling the truth. So its hearsay. Mark's text cuts off at the point where the women leave the tomb. An account considered to be the work of somebody else continues the story but as a clear instance of forgery it is not reliable. There is no reason to consider the faked Mark one as the first resurrection account and even if it were it would not count.

The next gospel Matthew gave us the first resurrection account and we read of Jesus appearing. It is riddled with absurdities such as asking us to believe the soldiers at the tomb were going to say that they slept on duty in order to pretend that Jesus's disciples stole the body. So far legend is not an option but the only option.
So the gospel tries to give historical data and Paul only gives a list but no detail.
It is not surprising then if there are problems with the first gospel detailing then there should be problems with Paul's contribution too!

He wrote, “I passed on to you first of all what I also had received that Christ died for our sins in accordance with [what] the scriptures (foretold), that he was buried, that he arose on the third day as the scriptures foretold, and [also] that he appeared to Cephas (Peter), then to the twelve. Then later he showed himself to more than five hundred brethren at one time, the majority of whom are still alive, but some have fallen asleep [in death]. Afterward he was seen by James, then by all the apostles (the special messengers), and last of all he appeared to me” (1 Corinthians 15:1-8).

The main problem is that it appears in a mess.  The evidence is thus ruined.  It loses its importance for it is not trying to give gospel style information and data.  The attempt to do that by Mark failed.  Plus Paul's text is too general.  It is only an account of what people thought not what is true.