Are duplicate pages that are never linked to bad for SEO?

I'm using WordPress and I added some rewrite functionality so that certain posts that normally have a link like:

http://example.com/category/post-name

Now look like:

http://example.com/special/path/post-name

But if you were to visit either link, the same content is served. Working on fixing this, but I'm curious if I should set up redirects or canonicals.

On my website, there are absolutely no references to the initial link, only the second link. My guess is that as long as there aren't links pointing to the old link, Google doesn't know about it and won't magically find it either, making 301s or canonicals more of a "just in case".

Is my thinking correct?