query: SELECT ?item (SAMPLE(?d) as ?d) (COUNT(DISTINCT ?person) as ?count)
  WHERE
  {
      ?person wdt:P509 wd:Q84263196 ; wdt:P31 wd:Q5 
      OPTIONAL { ?person wdt:P570 ?d .
               ?day wdt:P31 wd:Q47150325 ; wdt:P585 ?d 
               }
      BIND(COALESCE( ?day, wd:Q7883029) as ?item) 
  }
  GROUP BY ?item
  ORDER BY BOUND(?d) DESC(?d)