These are probably census records in Nederland:
* "Netherlands, Archival Indexes, Population Registers," , FamilySearch (https://familysearch.org/ark:/61903/1:1:Q2BQ-SSFL : 11 November 2017), Jan Willem Antonius Holtslag, ; from " Netherlands, Archival Indexes, Public Records," database, Coret Genealogie (www.genealogytoday.com : n.d.); citing Municipal Census, Steenderen, Gelderland, Netherlands, citing OpenArchives, Netherlands.
* "Netherlands, Archival Indexes, Population Registers," , FamilySearch (https://familysearch.org/ark:/61903/1:1:Q2BS-W78S : 11 November 2017), Jan Willem Antonius Holtslag, ; from " Netherlands, Archival Indexes, Public Records," database, Coret Genealogie (www.genealogytoday.com : n.d.); citing Municipal Census, Steenderen, Gelderland, Netherlands, citing OpenArchives, Netherlands.
* "Netherlands, Archival Indexes, Population Registers," , FamilySearch (https://familysearch.org/ark:/61903/1:1:Q2B3-P631 : 11 November 2017), Jan Willem Antonius Holtslag, ; from " Netherlands, Archival Indexes, Public Records," database, Coret Genealogie (www.genealogytoday.com : n.d.); citing Municipal Census, Steenderen, Gelderland, Netherlands, citing OpenArchives, Netherlands.
* "Netherlands, Archival Indexes, Population Registers," database, FamilySearch (https://familysearch.org/ark:/61903/1:1:Q2B3-J45V : 11 November 2017), Jan Willem Antonius Holtslag, ; from " Netherlands, Archival Indexes, Public Records," database, Coret Genealogie (www.genealogytoday.com : n.d.); citing Municipal Census, Steenderen, Gelderland, Netherlands, citing OpenArchives, Netherlands.
I don't know if those 4 are the same, there are other Holtslags that come up using Rootsearch/FamilySearch, mostly Neiderlandse records.