So if I already used Chirag's command to make my own backup, does that mean I've somehow tampered with the scheduled backups? That would not be good...
as already said only if your current scheduled backup includes a differntial backup. As differential backup includes all changes since last full backup.
If current schedule performs only full backup then COPY_ONLY makes no difference.
**I had a hunch that most production system (full recovery model) including yours use transaction log backup (which is most likely schedueld)**
