Thank you for reaching out to the Community about your contacts! I'm sorry to hear you're seeing a difference in numbers with your contacts. The email template you are working in (whether it be our older Legacy Newsletters or our newer Newsletter Emails) does not alter your contact lists. I have taken a look at one of your most recent campaigns and was able to determine the status on 13 of your contacts caused this difference. These contacts were set as either awaiting confirmation or on a temporary hold.
Contacts with this status type will not receive your emails unless they resubscribe or are taken off this hold. I hope this helps!