Script does not delete old backups due to the LEFT check

Description:

When running the backup script on a weekly basis (via cron schedule 0 0 * * 0), the older backups are not getting deleted as expected. The core issue lies in the LEFT check in combination with the BACKUP_NUM_TO_RETAIN value.

Steps to Reproduce:

1. Set BACKUP_NUM_TO_RETAIN to 4.
2. Run the script weekly.
3. Observe that after 5 weeks, there are 5 backups and none of the older backups have been deleted.

Expected Behavior:

After the number of backups surpasses the BACKUP_NUM_TO_RETAIN value, the oldest backups that exceed this count and are older than the DAYS_TO_RETAIN threshold should be deleted.

Actual Behavior:

Older backups are never deleted, regardless of their age, due to the LEFT check. Since we're only creating 1 backup per week and DAYS_TO_RETAIN is set to 4 days, the condition for deletion is never met.