Are you a film fan? Have you ever seen Braveheart? Pearl Harbour? Gravity? Interstellar? Bohemian Rhapsody?
What all these films (and a massive amount more) have in common is they get stuff wrong. History. Science - hard and theoretical. Even their own internal continuity.
Filmmakers often get things wrong. That's just a cold, hard fact.
The production team of 'Flash' can follow whatever the hell rules they like.
Doesn't mean they're getting it right.
Dude, I'm sorry to have to be the one to break it to you, but... time travel isn't real. There is no such thing as cold, hard facts with regards to time travel, because time travel doesn't really exist. Nobody knows how it would really work in reality, because it's never happened. So there is no "right" or "wrong" when it comes to how time travel works.