Thanks for your reply Angry Creative!
This is sort of an emergency so it's ok if the structure is a bit stiff, when we rebuild our site we'll do it right from the beginning. But right now we've got a blog running on example.com/blog built on a CPT and we need to set up another blog quickly. We would really like the URL to be example.com/blog/new_blog but I can't get this to work. This is what I've got:
blog (CPT with 'rewrite' => true)
blog-tags (non-hierarchical taxonomy with 'rewrite' => 'blog/blog-tags')
new_blog (CPT with 'rewrite' => 'blog/new_blog')
new_blog-tags (non-hierarchical taxonomy with 'rewrite' => 'blog/new_blog/new_blog-tags')
Everything works like a charm except the new_blog-tags taxonomy, the URL example.com/blog/new_blog/new_blog-tags/some-tag gives me a 404 error. Why is that?