I'm evaluating all of our leads that came in in 2014, and trying to determine where they came from (We do not have SFDC.) I use a Campaign Code field as a way to determine which campaign a lead came in through. However, an issue I'm having is if a lead is imported more than once. For example, if sales gives them to me as a conference lead, then on a later date supplies that lead on a list for an event invite. Every time I import a list and that Campaign Code is filled in, the original data (conference name campaign code) is override with the most current data (event campaign code).
Is there a way to lock a field so that information in a particular field won't change once it's filled in?