You need to decide what "duplicate" means in your case. If one person can ever have one counselor ever, then the index is the way to go. If a customer can have multiple interactions with the same counselor, then you need to change your table structure.

Have you ever gone into a store and they ask for your phone number, and you're like, "Why are you asking for my phone number? That's awfully personal information." The reason they do that is to track you as a unique customer because most people only have one phone number, especially nowadays when people have a cell number that's uniquely theirs. Unlike in the old days where a family might share a phone number, you can use something like that phone number to uniquely track people. That's why the IRS gave everyone a Social Security number. So, these checks you can do to look for someone's phone number or their address or whatever, but that's completely up to you.

When I would do would be to create a search form that your users can work with to try to find someone before they add a new record.