I was recently migrated from BTYahoo. I eventually found where my distribution lists had gone, but a few more addresses from my contact list seem to have been added for some reason. I can't work out how to delete these contacts from my distribution list without deleting the contact altogether.
Did your previous distribution list appear under the Contact groups?
If you delete a contact from the "Main" contacts, it will send it to the contact thrash folder. If you delete a contact solely through the contact group, it will remain in the "Main" contacts. I've been testing it out on my accounts to make sure everything is behaving as it should be 😁