Does the world really need to end of the 99th birthday?

In the “Back to the Future” movies Marty Mcfly goes back in time to 1955, then to 2015, and finally to 1985. So in 1985 he was from 2015. Which means in 2015 he was from 2045. Then his daughter had to send her kids back in time, which is unlikely in 2045 since cars can fly by then. Which means they never actually made those cars. Which means they never made those cars to send 2015 Marty to 1985. Which means they never actually made 1985 Marty go to 2015. Which means they never actually made 1985. <br>This is confusing.<br><br>Edit: typo: I meant his grandkids went back in time, not his daughter’s kids.<br><br>Edit 2: I have now been convinced that my math is bad, and my argument is invalid. 1985 is still here.<br><br>Edit 3: I have now been convinced that I’m just a terrible writer. 1985 has been here for 40 years, I’m just a bad storyteller. You should totally read my stories.