Have you ever faced a scenario where you have built search customization using Rest API with SPFx or custom display template in SharePoint 2013 etc which did not return all search results. I was facing this today while trying to get data based on a content type, it was returning only few results.
The reason is because Search API by default removes duplicates as documented by Microsoft. Items that are identical or nearly identical are removed from the result set.
https://docs.microsoft.com/en-us/sharepoint/dev/general-development/sharepoint-search-rest-api-overview#trimduplicates
Set the property trimduplicates to false on the Search API as below if there is a need
https://domainname/sites/sitename/_api/search/query?querytext=’contenttype:”the name of the content type”‘&trimduplicates=false&rowlimit=500&selectproperties=’Title’&sortlist=’LastModifiedTime:descending’
Hope it helps someone.
Mohamed Ashiq Faleel 
Thank you very much – this default option had an extreme impact on me, as instead of 150+ results I was getting only 5 (searching for all Document libraries in site collection).
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This is a hidden gem …Thanks so much for posting.
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