I ran into an issue where I needed to update over 1,000 contacts who were all on different (multiple) lists. There isn't a way to use a Header (i.e. Email Lists) so that when contacts are imported their lists are also updated. Instead you can only add them to one list. I highly recommend Constant Contact upgrade their system to also allow an Email List header so multiple contacts can be added to multiple lists in one bulk step. Thank you.