Actually there are as many gospels as there are favorable promises. 'Gospel' means good news. The good news to Abraham was'...
And he brought him forth abroad, and said, Look now toward heaven, and tell the stars, if thou be able to number them: and he said unto him, So shall thy seed be. And he believed in the LORD; and he counted it to him for righteousness.
(Gen 15:5-6)
The Gospel for the Israelites leaving Egypt was that they would be given a land flowing with milk and honey...unlike Abraham most failed miserably in believing.
Even though the basis of all salvation was based on the shed Blood of the Lamb, God dealt differently and had different promises to the Jews and to the Gentiles. But now through the revelation given to Paul...both Jew and Gentile are incorporated into the one Body of Christ through the free gift of grace apart from the law by ...That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.
(Rom 10:9)
and...Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand; By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain. For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
(1Co 15:1-3)
Now to him that is of power to establish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began, But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting God, made known to all nations for the obedience of faith:
(Rom 16:25-26)
Yes and there will come a tine when this Gospel dispensation ceases and the resumption of the promises (Gospel again) for a Messianic Kingdom resumes.
All dispensations were saved by faith but the object (promises) of that faith differed.
As a side, if you think it was the same Gospel today as it was in Noah's day, you'd better start trembling because only 8 were saved!! Instaed we find multitudes...After this I beheld, and, lo, a great multitude, which no man could number, of all nations, and kindreds, and people, and tongues, stood before the throne, and before the Lamb, clothed with white robes, and palms in their hands;
(Rev 7:9)
Thanks be to God for His unspeakable grace which is in His Son and which He chose Paul to reveal unto us believers today.