An exclusion list that had never matched a single file

The sitemap had a hand-maintained list of pages to exclude. It had never excluded anything. One side of the comparison carried a trailing slash and the other did not, so every check silently returned false and the list sat there looking like it was working.

The visible effect was two draft pages in the live sitemap and six indexable pages missing from it, for months.

A filter that matches nothing and a filter that is working correctly produce identical output when nothing should have matched. The only way to tell them apart is to assert the result against ground truth - here, the content collection itself - rather than trusting the list to be doing its job.