Find Duplicates works on an algorithm that is vulnerable to misspellings and different data. One misspelling or too specific of data can throw off the algorithm completely.
It is recommended when using this tool to start small and widen your search parameters. Try searching for one field that you're fairly certain would be the same or start the same as an existing record. We'll use an example of Eric Andre in our test system. Here's the information we know about Eric:
Unfortunately searching with all this info returns no results. But I'm not confident yet that it means we don't have a duplicate. So I'll try reducing information I search for. The best thing to do is search with just one field if you can, as this eliminates margin of error from other fields. We'll start with Last Name.
Looks like we found a potential duplicate, just from the last name! But the first name is spelled different. Easily a typo. To show the weakness of the algorithm, I'll try putting in the first name again spelled "Eric".
No results. This is because there's a different spelling. If I remove part of the first name from before the spelling is different though, I'll get a match again. This time I'll type "Eri"
That works! Hopefully this will help you understand that if First Name or Last Name are spelled differently from the results, the Find Duplicate search will not find the matching record, as they not spelled differently than your Search Query. Removing the "c" now returns Erik Andre as this record macthes the new Search query.
The Address field tries to match first on the Street Number. The system will find all matching Street Numbers as well as Street Names.
Hopefully this article helps you learn more about using the Find Duplicates tool and ensuring you find your duplicates more reliably!