screw you guys i wasn't done. anyways, don't assume 7 and 8 are right next to eachother because of their technology, and all the massive damage done to the earth and badada, it can all be dismissed with saying that a really really lot of time goes by between each one. heck, maybe the planet even collided with another one and became bigger, who knows?
so thats what keeps the theory possible, because time is what changes everything.
its possible for there to have been 8, then 9, then 10 because where 8 have lots of tech, where time passes and people turn midevil again, or the human race dies and comes back even, then eventually that crap dies out or whatever and 10 comes along with machina. see?
think way outside the box. like in the closet of the building across the street from the box making factory.