It seems on some setups Office 2016 limits the search items display to 75

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[HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Outlook\Search]

“SearchResultsCap”=dword:00000000

“DisableServerAssistedSearch”=dword:00000001

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SearchResultsCap overrides how many items are viewable in your search results. 0 is all.

DisableServerAssistedSearch disables the server-side search engine and uses your local computers search