Will the name of a person or address ever have a duplicate on data lists?

You have the ability to choose one contact per address, or multiple contacts for address. We always recommend one contact per address, especially with residential. If you're sending direct mail, you don't need to send multiple postcards to a house. The exception to this would be Business/Commercial lists. If you're looking for individual real estate agents, multiple people that work at the same company, a list of property managers, multiple people with the same job title at one company, etc. Residential nine out of ten times, it's one contact per address; however, depending on the business list you request or the specialty list, you could have multiple contacts in one office with the same job title.