Royal mail next day guaranteed delivery not delivered in time

Parcels was posted via Royal Mail next day guaranteed service on the 18 April 2017 from Nottingham and delivered to the recipient in Bolton on the 26 April 2017 which is 6 days late than the guaranteed time. This kind of things happen all the item so there is no such thing as guaranteed service. Below is tracking info by Royal Mail post office

Item:
AF059883898GB
Service
Special Delivery Guaranteed™
Latest update: Delivered
Your item with reference AF059883898GB has been delivered.
Delivered On:26-04-2017
Thank you for using our Special Delivery Guaranteed™ service.

Date Time Status Track point
26/04/17 18:52 RECIPIENT COLLECTED 26/04/17 BOLTON PDO
20/04/17 15:22 AT DELIVERY OFFICE BOLTON PDO
20/04/17 12:02 DELIVERY ATTEMPTED 20/04/17 BOLTON PDO
20/04/17 08:08 ON DELIVERY BOLTON PDO
20/04/17 06:13 AT DELIVERY OFFICE BOLTON PDO BOLTON PDO
20/04/17 04:34 ARRIVED AT MANCHESTER MAIL CENTRE MANCHESTER MAIL CENTRE
20/04/17 03:59 ON ITS WAY TO BOLTON PDO MANCHESTER MAIL CENTRE
19/04/17 20:09 ON ITS WAY TO MANCHESTER MAIL CENTRE NOTTINGHAM MAIL CENTRE
19/04/17 19:31 ITEM COLLECTED NOTTINGHAM MAIL CENTRE
18/04/17 17:16 SENT AT POST OFFICE 12 Park Farm Cen DE22 2QN