Remember that the way Paul describes the New Testament spiritual gift of prophecy is not canon-level revelation delivered infallibly and authoritatively like the Scriptures. The way he describes it, as I’ve argued elsewhere in more detail, is Holy Spirit-prompted, subordinate revelation that readers of 1 Corinthians 14 and 1 Thessalonians 5:19–21 would expect to be partially or fallibly reported, and therefore intended to be tested against and subject to the infallible, authoritative revelation now contained for us in the sixty-six books of the Holy Bible. Paul expects New Testament prophecy, the kind he refers to in 1 Corinthians 14, to be fallibly — which means sometimes erroneously — delivered by people. Mistakes will happen, which is why prophecy must be evaluated.
Far more detailed exegetical explanations have been made in the resources I’ve listed above, as well as in Wayne Grudem’s extensive book on New Testament prophecy and D.A. Carson’s Showing the Spirit.