I have a world where the average lifespan of 90% of the population is 120-150 years old and history is almost solely maintained in writing (so there are not really many visual recordings of past events).
Learning history is not particularly important for the vast majority of people either and there is no uniform way history is taught to children (if it's taught at all), only an elite few really study and/or maintain historical records. However, some of these elite few, the spiritual leaders of the world, do share history and historical lessons to the masses.
Given these parameters, is it safe to assume that a specific event happening around 1000 years ago could be considered "legend" or "lore" in the sense that even though people may be familiar with the story, the details are fuzzy and some don't even really think it happened (or perhaps think it's just a parable)?
I guess this would partially depend on the scope of the event, so let's say that it's a worldwide natural disaster, a flood that reshaped the continents in a matter of 2 days. 1000 years later, people know of the story of the flood and that's how the continents came to be how they are now because it's told by the spiritual leaders... but most people don't really believe that a 2 day worldwide flood really happened, as that seems impossible. Surely it's a parable or an exaggeration of what really happened.
Hopefully that example helps.
Edit: A couple of the answers made me realize that giving information on birth rates in this fictious place would help with answering the question.
To answer this:
People in this world tend to have children between the age of 30 and 50, mostly because women can strictly control when they conceive and men can control the gender, given this, there's no accidental births (or it's really rare) and so people tend to only have children when they've settled down and know they can take care of them (afford it) and don't tend to have that many children in general (although exceptions exist of course).