Wikidata SPARQL queries returning different results after filtering for English labels - sparql

Question

My understanding of Wikidata SPARQL queries is that you can filter results for English labels in two ways.
Adding SERVICE wikibase:label { bd:serviceParam wikibase:language "en" } to invoke a label service; or
Adding ?thing rdfs:label ?thingLabel FILTER (lang(?thingLabel) = "en") for every output label.
I am running a query where I'm trying to get all properties of an entity in English. I followed a Stackoverflow post and came up with two queries.
Query 1: Running this query takes returns 47 results.
SELECT ?itemLabel ?propLabel ?statement_property_objLabel
WHERE {
VALUES (?item) {(wd:Q24)}
?item ?property [?statement_property ?statement_property_obj] .
?prop wikibase:claim ?property.
?prop wikibase:statementProperty ?statement_property.
# Call label service.
SERVICE wikibase:label { bd:serviceParam wikibase:language "en" }
} ORDER BY ?propLabel
Query 2: Running this query returns 35 results.
SELECT ?itemLabel ?propLabel ?statement_property_objLabel
WHERE {
VALUES (?item) {(wd:Q24)}
?item ?property [?statement_property ?statement_property_obj] .
?prop wikibase:claim ?property.
?prop wikibase:statementProperty ?statement_property.
# Call label service for each label.
?item rdfs:label ?itemLabel FILTER (lang(?itemLabel) = "en") .
?statement_property_obj rdfs:label ?statement_property_objLabel FILTER (lang(?statement_property_objLabel) = "en") .
?prop rdfs:label ?propLabel FILTER (lang(?propLabel) = "en") .
} ORDER BY ?propLabel
Why is the second query returning fewer rows? Thanks for any help.

Answer 1

I think the cause is that the wikibase:label service returns label results for any value of ?statement_property_obj, even if that value has no actual rdfs:label defined (it appears to just return the actual value of ?statement_property_obj itself).
As an example, see the very first result in query 1, where ?statement_property_objLabel is bound to topic/Jack_Bauer. This is not the value of an actual rdfs:label property in the data, just a 'fallback' value that the label service provides. So query 2, which explicitly queries for rdfs:label attributes, won't return this (and similar) results.