The Deep Search will use the data you provide to try and return you the most probable profile it can with as much data it can find. The ultimate goal is to return you a single personal profile but there will be cases when the results are not very clear as to who exactly you are looking for so then the Deep Search might return several profiles.
For example, if you are seeking John Smith who works/worked at Microsoft, Deep Search will probably return more than one profile as there is probably more than one John Smith who works at Microsoft or has worked there in the past.
What are the 'must haves'?
You can be selective of the data you want to be returned. You should define what data is your 'must have' when Deep Search returns a response. If it is an email that you are seeking, then be sure to check the 'Email' checkbox of the 'must haves.
**Note that emails only show when the Deep Search finds a single matching profile.