The Catholic Catechism, para 67 (LINK) says private revelation "does not belong to the deposit of faith."
My point is that one of you says it is private while the other seems to claim otherwise.
Listen to the sermon, It discusses what I am pointing out. It is Fact that it Happen. This is not arguable. Now if you wish to not believe in the message that was sent that is your prerogative however the Miracle of the Sun at Fatima and the other apportions did occur, there were witnesses, it was documented, and that are the Facts.
One can deny the fact/s as exampled in the sermon but that just means they are fools, unwilling to accept Known Truth. The example given was the Alamo, were you there? No but you know it happen? Yes, because it did occur, there were witnessed, it was documented, and that are the Facts Note at Fatima there were many, many more witnesses than the Alamo.
God Bless
For context I've posted the verses you noted though I did post a bit more from 1 Corinthians for context.
1Now I make known to you, brethren, the gospel which I preached to you, which also you received, in which also you stand, 2by which also you are saved, if you hold fast the word which I preached to you, unless you believed in vain. 3For I delivered to you as of first importance what I also received, that Christ died for our sins according to the Scriptures,4and that He was buried, and that He was raised on the third day according to the Scriptures, 5and that He appeared to Cephas, then to the twelve. 6After that He appeared to more than five hundred brethren at one time, most of whom remain until now, but some have fallen asleep; 7then He appeared to James, then to all the apostles; 8and last of all, as to one untimely born, He appeared to me also. 1 Corinthians 15:1-8 NASB
13But we should always give thanks to God for you, brethren beloved by the Lord, because God has chosen you from the beginning for salvation through sanctification by the Spirit and faith in the truth. 14It was for this He called you through our gospel, that you may gain the glory of our Lord Jesus Christ. 15So then, brethren, stand firm and hold to the traditions which you were taught, whether by word of mouth or by letter from us. 2 Thessalonians 2:13-15 NASB
This sure seems to support sola scriptura which is the position advanced by Christianity. All that we need for salvation has been revealed in His Word, Jesus Christ.
The Apostles did not advance anything beyond what we have as the written Word.
These seems to call into question any of the ex-cathedra statements issued by the Pope, especially those concerning Mary, as we seen none of the catholic marian doctrines in the Old or New Testament.
There are no admonitions to pray to mary or to rely upon mary for our salvation as these would contradict the Gospel message especially relying upon Mary for salvation and/or forgiveness of sins. The Word clearly teaches it is only through faith in Christ that we have forgiveness of sins. John especially emphasizes this in his Gospel and 1-3 John. None of the Gospel writers nor Paul, or Peter reference Mary with any capacity or role in our salvation or forgiveness of sins.
There are admonitions against idols of which a lot of catholic churches have one of "mary".
The Mary as recognized by the roman catholic church is not the Mary as found in the NT.