The semantics of RDF identifiers drift at least as often as HTML format changes.

For example, at one point I was doing a similar thing against DBPedia (a sort-of predecessor to WikiData).

I was doing leaders of countries. But it turns out "leader" used to mean constitutional leadership roles, and at some point someone had decided this included US Supreme Court Chief Justice (as the leader of the judicial branch).

So I had to go and rewrite all my queries to avoid that. But most major countries had similar semantic drift, and it turned out easier to parse Wikipedia itself.