Why can’t we go back to Creation?

I’ve seen you write in a few places about dates before the 1700s BCE not being accurate because of 10 days added. But the days went from Wednesday to Thursday being the next day.. so if all cultures including our culture still kept a 7 day calendar, shouldn’t we be able to zoom out and go back 5785 years ago and see exactly to this day, what day of the week it was on day one?

We would be using the Jewish year and cycle, and the Wednesday to Thursday change shouldn’t effect anything because it’s still accurate within the days of the week.