I agree, its confusing how I explained it, but its actually very simple. The 7 trumpets are chronological, up until the 7th trumpet. Then you start all over and get another aspect of the past, present and future in chronological order from the 7 seals. They are somewhat parallel prophecies. Same thing with the 7 churches. The 7 churches, 7 trumpets, the 7 seals are all somewhat parallel, representing the entire Christian dispensation. In all cases, after you pass the 7th, Jesus comes thereafter.
In regards to how we can know whats past and what is future. It is no different from the statue of Dan 2 and the four beast of Dan 7. They are parallel prophecies. In dan 2, we know the head of Gold represents Babylon (the beginning of the prophecy) and the Rock cut out hands is God's everlasting kingdom (the end of the prophecy). With that knowledge, we can trace history down to discover the meaning of the rest of the prophecy in Dan 2. The same concept applies to the 7 churches, 7 trumpets, 7 seals.
I understand what you are saying, but there is another way to look at this.
There are 7 Seal judgments. The 7th Seal judgment is the next set of judgments which are the trumpets and the 7th trumpet is actually the next 7 judgments which are the vial judgments. Looks like this...............
1st Seal
2nd Seal
3rd Seal
4th Seal
5th Seal
6th Seal
7th Seal is then the next set of 7 Judgments which are the Trumpets
1st Trumpet
2nd Trumpet
3rd Trumpet
4th Trumpet
5th Trumpet
6th Trumpet
7th Trumpet is actually the next 7 set which are the Vials.
1st Vial
2nd Vial
3rd Vial
4th Vial
5th Vial
6th Vial
7th Vial = Armageddon
Revelation 16:17
"And the SEVENTH angel poured out his vial into the air and there came a great voice out of the temple of heaven saying...."It is done".
Chapter 17 and 18 are "Parenthetical" and then the chronological order resumes in chapter 19 with the literal coming of Christ.