The summary of the content of the Gospel is stated about 24 years after the death of our Lord Jesus Christ
.
1Cor.15 1] Moreover, brethren,
I declare unto you the gospel
which I preached unto you,
which also ye have received,
and wherein ye stand;
[2] By which also ye are saved,
it ye keep in memory
what I preached unto you,
unless ye have believed in vain.

This was the main focus of his preachng, the primary teaching , first of all,
consisting of which are three points.

[3] For I delivered unto you, "first of all."
that which I also received,
how 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:

how that Christ died for our sins, must be given special notice, since it explains the focus of the death of the Lord Jesus Christ

Paul specifically refers to "Christ died for our sins" referring to himself and the Corinthian believers, he calls this the Gospel, and says nothing concerning Christ's death being sufficient for all, made available for all, provided salvation for all, or even was intended for all.

Of course this does not apply to these two groups only, "himself and the church at Corinth."

In Acts 20:28 Paul clarifies that it applies to all of those secured by Christ's death by referring to them this way, "he hath purchased the church with his own blood." Again the death of the Lord Jesus Christ, was specific, focused, and particular as to its intention.

Paul says this is the message that saves. So the question is, can another message be the Gospel, than the one which Paul refers to. Of course not