Different Lists, Different Information

So I have 3 different lists that each collects different information.  But, when I add a custom column to one, the column is included in the other. Just to understand better, I do have some contacts who appear on multiple Contact Lists. This morning, I made a new contact list with different data.  When I uploaded the spreadsheet, the new contact list pulled data from the 1st spreadsheet when that data should not be included. I don't understand what I am doing wrong. I didn't map that data. I don't understand that, if I have 2 different lists why 1 would pull data from the other and how do I correct that?