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Using rsync for incremental backup, what happens when original full backup is due for deletion?

I have started an incremental back up, on an external hard drive, of my Fedora 20 data etc using the scheme from here, which produces a full back up on day 1 followed by incremental backups using hard links on following days, so that only changes are recorded. I intend to keep 28 days backups, by deleting each as it becomes 28 days old. My question is: please what happens when the original full backup up becomes the next to delete. It seems to to be possible that then there is nothing left to link back to. Surely I have not appreciated fully what happens, but this is not explained in the excellent site quoted, and my understanding of it is not sufficient for me to predict what will happen.