Whatever Cronos' and Ann's version of the Gospel might be, we now hear that it is far, far larger than all of the four Gospels in the New Testament combined. That might explain why we never hear it.
I don't think that's the reason, however. I think the reason is shame. To paraphrase some earlier posts:
"What is it with Catholics that they cannot answer that question?? Really....have you EVER known a Protestant that couldnt answer what the Gospel is?? Catholics must be ashamed of the Gospel!"
You presume much and are in great error when you say Catholics are ashamed of the Good News of Jesus Christ.
The Gospels in the Written NT Scripture are the 4 books Matthew, Mark, Luke and John. Your claims of that not being so are not going to change historical accepted fact. Now as to what Good News the authors of the Epistles refered to it would be what Jesus taught them and how and why He came for our salvation. These things are contained in the Gospels of Matthew, Mark, Luke and John. Jesus Himself not only came to give the Good News. He is the Good News. He is the embodiment of the Gospels. The Living Word, The Logos. Apart from Him, there is no Good News.
As I answered before:
Gospel means good news. Epistle means a letter. The gospels are narratives of the life and words of Jesus. Matthew, Mark and Luke are the synoptic gospels. The Gospel of John is a non synoptic gospel.
As for specifics of the good news, Luke 4:18-21 is probably as good a summary as any.
18(A)THE SPIRIT OF THE LORD IS UPON ME,
BECAUSE HE ANOINTED ME TO PREACH THE GOSPEL TO THE POOR.
HE HAS SENT ME TO PROCLAIM RELEASE TO THE CAPTIVES,
AND RECOVERY OF SIGHT TO THE BLIND,
TO SET FREE THOSE WHO ARE OPPRESSED
19(T)TO PROCLAIM THE FAVORABLE YEAR OF THE LORD.
20And He (U)closed the book, gave it back to the attendant and (V)sat down; and the eyes of all in the synagogue were fixed on Him.
21And He began to say to them, Today this Scripture has been fulfilled in your hearing.
FWIW, we live to be able to tell unbelievers The Gospel. We support missionaries in some of the darkest areas of the world so they can tell people The Gospel. These same missionaries are being persecuted and killed for preaching The Gospel.