There is a ‘Region’ Filter and a ‘Tags’ taxonomy reference field, which are also used in other content types.
We only wanted to show used terms in the drop downs.
So, there are other pages (Views) that also implemented this tag as a filter (like the Alumni page). But of course: those pages have other content types, so ‘used tags’ are also different.
So here is how we limited the used tags, per Drupal View, this article gave us a kickstart.
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