If a student is in PowerSchool Enrollment and doesn't have a Snapcode, it's because their parent #1 email was either missing or invalid so they didn't get an email sent which generated the Snapcode.
Printing the letter or sending the email actually generates the Snapcode. So if a student is in PowerSchool Enrollment without a Snapcode listed, here is what you need to do:
Now when you go back to the Roster Workspace, those students will not be under the Imported/Added view but instead in the Notified/Not Started View and will have a Snapcode listed.