The Olivet Discourse does not describe End Times events in a strict-and-straight-forward chronological order.
The most obvious indication of this is the phrase "But before all these" in Luke 21:12.
You disregard the complete context of the scripture, Gary anybody can pull a verse out of the Bible and build a religious following.
As the complete context states, the signs given will be signs of the (Season) and those that see it will not pass (Generation)
Gary you aren't going to create 1950+ years of desolations and tribulations from the verses below, just give up to God's truth
Signs, Season, Second Coming, Not 1950+ Years.
Matthew 24:15 The AOD (Future)
Matthew 24:21 The Great Tribulation (Future)
Matthew 24:29-30 The Second Coming Of Jesus Christ (Future)
Luke 21:29-32KJV
29 And he spake to them a parable; Behold the fig tree, and all the trees;
30 When they now shoot forth, ye see and know of your own selves that summer is now nigh at hand.
31 So likewise ye, when ye see these things come to pass, know ye that the kingdom of God is nigh at hand.
32 Verily I say unto you, This generation shall not pass away, till all be fulfilled.
Matthew 24:32-34KJV
32 Now learn a parable of the fig tree; When his branch is yet tender, and putteth forth leaves, ye know that summer is nigh:
33 So likewise ye, when ye shall see all these things, know that it is near, even at the doors.
34 Verily I say unto you, This generation shall not pass, till all these things be fulfilled.