There is only one gospel in this dispensation and in 1 Corinthians 15:1-4, Paul clearly states: 1 Moreover, brethren, I declare to you the gospel which I preached to you, which also you received and in which you stand, 2 by which also you are saved, if you hold fast that word which I preached to you--unless you believed in vain. 3 For I delivered to you first of all that which I also received: that Christ died for our sins according to the Scriptures, 4 and that He was buried, and that He rose again the third day according to the Scriptures.
In Ephesians 3:1-9, Paul clearly states: 1 - For this reason I, Paul, the prisoner of Christ Jesus for you Gentiles— 2 if indeed you have heard of the dispensation of the grace of God which was given to me for you, 3 how that by revelation He made known to me the mystery (as I have briefly written already, 4 by which, when you read, you may understand my knowledge in the mystery of Christ), 5 which in other ages was not made known to the sons of men, as it has now been revealed by the Spirit to His holy apostles and prophets: 6 that the Gentiles should be fellow heirs, of the same body, and partakers of His promise in Christ through the gospel, 7 of which I became a minister according to the gift of the grace of God given to me by the effective working of His power. 8 To me, who am less than the least of all the saints, this grace was given, that I should preach among the Gentiles the unsearchable riches of Christ, 9 and to make all see what is the fellowship of the mystery, which from the beginning of the ages has been hidden in God who created all things through Jesus Christ.
This is the "good news" that the apostle Paul preached after the cross, but does this share the exact same content as the "good news" that the twelve, John the Baptist, and Jesus Christ were preaching before the cross? They were still preaching the "good news" gospel of the kingdom to Israel. This is where it gets a little deep.
If the gospel of the kingdom, prior to the cross has the exact same content as the gospel of grace after the cross, then Matthew 10:5-7; 16:21-22; Mark 16:14; Luke 18:31-34; 24:19-24, 44-47, along with Ephesians 3:1-9 are superfluous verses. Before the cross, the gospel of grace that Paul taught and came to him through a revelation of Jesus Christ (Galatians 1:11-12) was said to still be a mystery.
I've heard certain people say that the gospel Paul preached was preached as far back as Moses and even Adam, yet I see no evidence in scripture for this. I've heard people confuse the gospel "good news" of the death, burial and resurrection of Christ with everything that is written in the 4 gospel accounts. Some people call the entire Bible the gospel and Mormons have added the Book of Mormon to the Bible and call that the "fullness" of the gospel, so as we can see there is much confusion out there in regards to what the gospel is and there are those who pervert the gospel by teaching salvation by "grace plus law, faith plus works." (Galatians 1:6-9)