Seed list behaviour

If your seed list disappears, there are two possible scenarios:

The simple scenario (when the email is setup as the unique key)

The contacts you are trying to add in the seed list are already included in your population whether they are in a filter, list or other population you added to your scenario. If the contact is already existing in another population it will not be added; therefore, the number of contacts in the seed list wont' match the number you've entered.

During campaign creation

After campaign creation

The complex scenario (the email field is not the unique key, but a custom field (c2))

The seed list is being added one by one in the campaign's table. In this table (internally) there is a unique key that matches the client's unique key. In this case, it's the custom field c2.
When the user adds the seed list, only the email is mandatory (not the c2 field). Therefore, when the platform adds the contacts in the campaign, three different situations can happen:

1.- The seed list contact exists in the clients DB: in this case the platform checks the c2 from the DB and inserts it eventually in the internal table of the campaign.

During campaign creation

After campaign creation

2.- There is one contact in the seed list that is not in the client's DB: once the platform has checked the information in the DB, (as c2 is not a mandatory field), the contact will be added with an empty value in the c2 field in the internal table of the campaign.

During campaign creation

After campaign creation

 
3.- There are 2 (or more) contacts in the seed list that are not in the client's DB: once the platform has checked the information in the DB, the contact will be added with an empty value in the c2 field in the internal table of the campaign.
However, if there are 2 (or more) contacts with blank information, the platform will remove those contacts because the seed list cannot have more than one empty unique key.

During campaign creation

After campaign creation