Honestly, that's sensible. Is there a way to get your brain to compromise to a level of vaguery?
Like, if there was a reality changing event 5000 years ago, it would make complete sense that things would be an unknown from that time period. Unless the story is about archaeologists or very long-lived characters, it may not have an impact on the story.
Think about IRL, 5000 years ago is around when they were inventing cuneiform writing. We don't have a good understanding of what happened back then, and it really doesn't have any impact on the things that are happening now. Is that different in your book?