If a date was missed, the job will run as soon as possible.
Storage options
Nothing will be deleted. The backup size will grow with each change. When the storage limit will be reached, there won't be new backup. You will be notified by a failed backup in the backup report.
Over time backups will be deleted automatically. There will remain one backup for each of the last 7 days, each of the last 4 weeks, each of the last 12 months. There will always be at least one remaining backup.
Once there are more backups than the specified number, the oldest backups are deleted.
If at least one newer backup is found, all backups older than this date are deleted.