County Records with no sale info

[DuWayne Jones]

I'm combing through online County records in an area of Minneapolis that I'm planning to market to, and have come across several properties with no information identified for a previous sale.  Does this mean there is no recorded mortgage? I'm wondering if this is a clue to potential equity in the property, or if it could mean something else.  My goal is to look for properties that were sold 15 or more years ago.  Any advice or help is greatly appreciated.  Thanks!