Question : When importing my lists, I see my dynamic columns already created with other contact imports. Can they be used for a new import of lists?

Answers : Yes, dynamic columns, already created with other contact list imports, are common to all lists. You should use them and not recreate new identical columns.

The advantage is to limit the number of dynamic columns and also to obtain better overall statistics from your campaigns

To manage your dynamic columns, you will find them here https://application.magileads.net/configurations/data-fields
Or in the »Configurations » tab -> dynamic columns