Last Activity Dates

I successfully installed the Add-On yesterday, and I placed the four Activity Fields in the Record Layout where they are not likely to be seen by many users. After opening a few Account and Contact Records I noticed that many had no data in the four fields. I selected the "Populate Missing Dates" option in the Admin section, hoping it wouldn't impact performance too much. It doesn't . Maybe because the fields aren't being populated until a call or email is recorded. Currently, there are only 111 Accounts and 135 Contacts with any data in the fields. I'm looking for information on how I can get the fields populated on all records so the Reports we desire will be accurate. How are the updates triggered if not with the "Populate Missing Dates"?