External search engines should, but do not always send readers straight to the right page. They send readers to the pages with the highest ranking according to the algorithm used. However that can give the wrong thing certain circumstances - such as if a webpage is moved, without the old title continuing to point at it. That's because the incoming links which are a major contributor to page ranking will continue to point to the old title (we can only fix internal links). 
 :::The Durham move was such a case, as UK readers no longer find the article about the city, they find the dab instead. Meanwhile US users are unaffected as the NC city still dominates their searches. If Worcester is moved, the same negative impact will hit UK users after this article, with no positive benefit to US users after info on the MA city. 
 :::To be honest, I think WP:PRIMARYTOPIC itself is wrong - if guidance advocates breaking of stable URLs then its bad guidance. We are not constructing a brand new resource, but maintaining an existing one. In the abstract, we would choose the most significant to be at the basename. However, once that choice has been made and the article locations are settled, no one really cares. If we consistently used wikidata codes you could still find the article.anion