Updated: Oct 24, 2018
Time is a tricky thing to worldbuild for me and I have been tempted in my own writings to write past events as "500 years ago." It's a nice round number and it sounds like a long enough period to experience a cataclysmic event, start recovering from said event, and still have accurate records of that event.
Then I started doing more detailed research into the different eras of history and I came to realize that 500 years is a really really long time.
500 years ago, Martin Luther posted his Ninety-five Theses, the Caribbeans had just been discovered, even things that an American would consider foundational to reality would have been unheard of in that period of history.
And these are just some of the examples from one segment of the world. Even counties that have had a long life have gone through huge changes in that period, up to and including being conquered, having a huge number of their population killed, or inventing new technology.
I eventually knocked the timeline down to 100 years. It's a long enough period of time for a region to recover and start stabilizing, but still be isolated and dealing with issues. The events that led to the cataclysm probably wouldn't have been written down, but there would still be second hand accounts and "My grandma use to talk about-" 's that could be relayed to the main character. It would also allow for longer lived beings to still be emotionally invested in the cataclysm and act as either antagonists or as supporting characters, if they aren't the main character.