Are legendary items found in the world a one time item?

There are some YouTube videos which show the location of certain legendary items in the world, and where to find them.

I found one through exploration and soon out levelled it and ended up selling it. It seems legendary items drop at your current level. I know I can upgrade them, but I do not have any legendary crafting materials just yet.

Once I've collected them are they gone forever?

Solution 1:

Yes they are. Legendary items looted from world caches are a one time deal.

I looted a Legendary Monowire a few days ago.

When I returned to the chest where I found it today, the chest was open.

This would mean that if you do use a YouTube video to loot legendary items from the world they will be dropped at your current level, and you'll outlevel them unless you upgrade them.