Why does my import only add part of my list?

Hi, I'm attempting to create a new list with an import from our CRM. There are 10K names/email addresses on this list, but only a portion of them are being imported. Several thousand already exist in constant contact (with permission to send) but they are not being found and added to this new list. I'm not sure if something has changed in the last 6 weeks since I've added a new list with how permissions are treated.