The argument is advanced that since Revelation 11 was written about 40 years after 1 Corinthians 11, that Paul could not have been referring to Revelation 11 with his phrase "last trumpet" because that scripture had not been written yet. The conclusion is therefore reached that it must refer to a trumpet referred to earlier, which they use to buttress their arguments for the application of this scripture to the trumpets that are blown during the Feast of Trumpets. There are three sets of nine trumpet blasts each during that feast.
I do not believe this is a convincing argument. I believe it is permissable for Paul to refer to a last trumpet, and for that reference to be explained in further detail, forty years later, by the Revelation to John. He is hearing the Lord talking about it. The truth of the Book of Revelation was already known to the Holy Spirit.
The Spirit of God has done this in other places. Daniel saw the ancient of days, coming on the clouds, and reported it in Chapter 7, verse 13-14. This receives further explanation in Revelation 1:7, where it is explained by Jesus, speaking to John, that also those who pierced him will see him, and the kindreds of the Earth will wail because of him.
It is common for later passages of the bible to amplify an earlier passage.