Thanks for reaching out to us, I'd like to offer some insight on the Resend To and Resend-to-Non-Openers (RSNO) functions.
When using the Resend To, because you're essentially doing an original send-out of the same email, it's effectively coded the same way. This is why in the reporting data will show them as all the same group as the original send's reporting. These people can still technically receive a previously established RSNO.
When using the RSNO, because of its separate coding, and because so many customers find it important to keep track of the number of people who require additional sendouts, it is considered different from the original sendouts for reporting data.
In both these iterations our system makes sure to only send to applicable contacts. Resend To only goes to contacts added after the initial send to a list, and RSNO only looks for those who've been sent the campaign and haven't opened it.
Please note with the Resend To, if you choose the option to copy your campaign, you are effectively making a brand new campaign that could be sent out to the full list.
If you have any additional questions or concerns, feel free to reply to this thread or open a new one, and we'd be happy to assist.