If this affected all links, couldn’t you just monitor it with a general “does downloads of these URLs work” check? You don’t have to (and shouldn’t) monitor 404

If this affected all links, couldn’t you just monitor it with a general “does downloads of these URLs work” check? You don’t have to (and shouldn’t) monitor 404 returns to test whether downloads are working, the naive and obvious test is to actually attempt to download something.