When looking at the list of backups you can restore from, this is what's available for you:
The five most recent backups;
concerning the fifth most recent backup, all backups on the same or prior day;
the most recent backup per day for the previous seven days;
the most recent backup per week for the previous three weeks;
the most recent backup per month for the previous three months.
If you created a backup a year ago and since then you haven't created any new backups, that old backup will still exist, but as soon as a new one is completed, the older one gets scheduled for deletion. This is why it isn't possible to restore a backup from a year ago if new backups have been recently created.
Meant to merge your old backup with new content? Learn more about why that isn't possible, here.