sparql - Some cities aren't instances of city or big city? Odd behaviour of Wikidata

Question

While examining the results of the official example query "Continents, countries, regions and capitals" (on https://query.wikidata.org/, limited to Germany for your convenience here: link), I noticed that some capitals of German federal states were missing. For example Wiesbaden as capital of Hesse. I noticed that Wiesbaden is an instance of big city, but not of city (see https://www.wikidata.org/wiki/Q1721), in contrast to some other cities. I was able to alleviate the problem by also including cities that are subclasses of city by changing line 17 to ?city wdt:P31/wdt:P279? wd:Q515.
One of the four cities that are still missing is Magdeburg, the capital of Saxony-Anhalt.
The diagnostic query

SELECT ?cityLabel ?props
WHERE {
  ?city wdt:P31 ?props.
  FILTER(?city = wd:Q1733 || ?city = wd:Q1726).
  SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }
}

shows that Magdeburg is not even an instance of city, although it clearly is according to its Wikidata page https://www.wikidata.org/wiki/Q1733.

I am new to Wikidata and SPARQL. However, this seems wrong to me. What can I do to get all capitals of the german federal states? And what is the reason for this behaviour?

Answer 1

These missing statements are not truthy:

SELECT ?statement ?valueLabel ?rank ?best
WHERE {
  wd:Q1733 p:P31 ?statement.
  ?statement ps:P31 ?value .
  ?statement wikibase:rank ?rank .
  OPTIONAL { ?statement a ?best . }
  SERVICE wikibase:label { bd:serviceParam wikibase:language "en". }
}

Try it!

They are normal-rank statements, but there is a preferred-rank statement.

Truthy statements represent statements that have the best non-deprecated rank for given property. Namely, if there is a preferred statement for property P2, then only preferred statements for P2 will be considered truthy. Otherwise, all normal-rank statements for P2 are considered truthy.

Update

I have decreased the rank of the preferred statement just now. Please test your query again.