1. Go to https://query.wikidata.org/ and send the following SPARQL Query
<pre>
## Frage nach Physiker, die eine Seite auf de.wiki und en.wiki haben, und ordne
# das Datum nach dem Geburtstag im Jahr
#
#SELECT ( COUNT(?item) as ?numberOfPhysicists ) # result 4981 (in 28s) at 2019-09-08
#
SELECT DISTINCT ?item ?itemLabel ?sitelink (YEAR(?date) as ?year) ?date
WHERE
{
?item wdt:P106/wdt:P279* wd:Q169470. # Tätigkeit '?classPhys', mit "property path" S 62-65
?sitelink schema:isPartOf <https://de.wikipedia.org/>;
schema:about ?item.
?site2link schema:isPartOf <https://en.wikipedia.org/>;
schema:about ?item.
?item wdt:P569 ?date .
BIND( 100*MONTH(?date) + DAY(?date) AS ?monthday )
BIND( YEAR( ?date ) AS ?xyear )
FILTER( ?xyear < 1580 )
SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }
}
ORDER BY ?monthday
LIMIT 6000
</pre>
2. send search in the result list "wd:Q619", that is Nikolaus Kopernikus,
3. The birthday of Nikolaus Kopernikus is shown to be the 28. Februar 1473
4. Now select the page "https://www.wikidata.org/wiki/Q619" the property "P569" (date of birth) shows 19 February 1473 which differs from the number in the result list by 9 days.
5. This error happens also with other persons and with the date of death
6. To me it seems that this error ist related to a wrong handling of Julian and Gregorian calender, may be in the MONTH- and DAY-Function of the SPARQL- implementation and in the formating of dates in the SPARQL-result- list.
I hope a correction will soon result to the same and correct date values for dates earlier than 1580
See also the discussion in the German Wikipedia
[https://de.wikipedia.org/wiki/Wikipedia_Diskussion:Redaktion_Physik/Wikidata-Abfragen#Todestag_von_Kopernikus Wikidata-Abfragen#Todestag_von_Kopernikus]