Where do I get the idea you are a pre-tribber; from prior posts on this and other message boards where you profess a pre-trib position.
Revelation 7:1-8
2 And I saw another angel ascending from the rising of the sun, having the seal of the living God; and he cried out with a loud voice to the four angels to whom it was granted to harm the earth and the sea, 3 saying, "Do not harm the earth or the sea or the trees, until we have sealed the bond-servants of our God on their foreheads." 4 And I heard the number of those who were sealed, one hundred and forty-four thousand sealed from every tribe of the sons of Israel: 5 from the tribe of Judah, twelve thousand were sealed, from the tribe of Reuben twelve thousand, from the tribe of Gad twelve thousand, 6 from the tribe of Asher twelve thousand, from the tribe of Naphtali twelve thousand, from the tribe of Manasseh twelve thousand, 7 from the tribe of Simeon twelve thousand, from the tribe of Levi twelve thousand, from the tribe of Issachar twelve thousand, 8 from the tribe of Zebulun twelve thousand, from the tribe of Joseph twelve thousand, from the tribe of Benjamin, twelve thousand were sealed.
NAS
Read Revelation 7:2ff in context and your use of vs. 2 & 3 does not support your thesis.
Once again (and maybe this time you will respond with an answer), what is a genuine believer, which by the way is just another way of stating "they were never saved in the first place".
Romans 10:1-15
10:1 Brethren, my heart's desire and my prayer to God for them is for their salvation. 2 For I bear them witness that they have a zeal for God, but not in accordance with knowledge. 3 For not knowing about God's righteousness, and seeking to establish their own, they did not subject themselves to the righteousness of God. 4 For Christ is the end of the law for righteousness to everyone who believes. 5 For Moses writes that the man who practices the righteousness which is based on law shall live by that righteousness. 6 But the righteousness based on faith speaks thus, "Do not say in your heart, 'Who will ascend into heaven?' (that is, to bring Christ down), 7 or' Who will descend into the abyss?' (that is, to bring Christ up from the dead). " 8 But what does it say? "The word is near you, in your mouth and in your heart"-- that is, the word of faith which we are preaching, 9 that if you confess with your mouth Jesus as Lord, and believe in your heart that God raised Him from the dead, you shall be saved; 10 for with the heart man believes, resulting in righteousness, and with the mouth he confesses, resulting in salvation. 11 For the Scripture says, "Whoever believes in Him will not be disappointed." 12 For there is no distinction between Jew and Greek; for the same Lord is Lord of all, abounding in riches for all who call upon Him; 13 for "Whoever will call upon the name of the Lord will be saved." 14 How then shall they call upon Him in whom they have not believed? And how shall they believe in Him whom they have not heard? And how shall they hear without a preacher? 15 And how shall they preach unless they are sent? Just as it is written, "How beautiful are the feet of those who bring glad tidings of good things!" NAS
A "genuine believer" is one who confesses with his mouth and believes in his heart that Jesus Christ is Lord. And regardless of what you have tried to prove (without success) is that "genuine believers" can and do cave under tribulation, which is what both Jesus and Paul have stated in plain terms will happen.
You see (Omega) only a "genuine believer" can become an apostate, which means they have fallen away from the faith resulting in loose of their salvation, another Biblical fact you have simply ignored in a vain attempt to promote a false doctrine.
2 Thessalonians 2:3-4
3 Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition;
4 Who opposeth and exalteth himself above all that is called God, or that is worshipped; so that he as God sitteth in the temple of God, shewing himself that he is God.
KJV
This one section of Scripture totally defeats and disproves OSAS, and I will save you the trouble of looking up the only other NT verse that uses the Greek word translated “falling away”: Acts 21:21
21 And they are informed of thee, that thou teachest all the Jews which are among the Gentiles to forsake Moses, saying that they ought not to circumcise their children, neither to walk after the customs. KJV