... WordPress can automatically detect duplicate post titles within the database and append a dash with a number to the end of the post title.

I do notice that when I try to use the same child category-term beneath different category-parents, WP automatically modifies the category-slug in this manner (by appending a dash-#), which then generates modified permalinks (while leaving the identical child-terms themselves untouched).

This results in a modified suggest permalink, ie:

Two category-trees, geo > alaska > rivers > wild and hike > olympic > rivers > wild become URLs geo / alaska / rivers-1 / wild-1 and hike / olympic / rivers-2 / wild-2 (without spaces).

As a result, I resist the inclination to use "obvious" recurring category-terms beneath independent category-hierarchies ... where indeed the paths themselves are perfectly "unique". The category names aren't changed, only the recommended slug (which you can make different in your own manner of chosing), and thus the subsequent URL.

A separate case, with a similar result.