Linking to articles is always a good idea, but if old content already generates traffic it's always best to update that specific article, and keep it up to date, instead of creating new, similar/related ones.
In the best of worlds, we actually want both as it would benefit us more than just one of them.
If you come across a great article though, and you feel that the old content you know of would make a good addition to the newly one, you should definitely include a link to it. It goes both ways.
New content? - Include links to old content.
Old content? - Include links to new content.
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