I feel Royal Mail aim for deniability. Number not in the system so can’t prove or disprove and just claim the system lost the code. Until it’s actually confirmed delivered then if by magic it’s in the system.
Used to send letters recorded signed for to prove a company received them, but RM would just say they have no record of a signature. Likewise had postie deliver stuff to me requiring signature but tore off the label and dumped on the doorstep. Asked RM for proof of the signature and they said they can’t find it, system must have lost it.
Had an Amazon Now delivery last week, gives me a map showing where the guy is, text updates, he arrives and greets me by first name, sign and he leaves and within a 1 minute I get a text saying it’s been delivered.
Another one (I forget the courier) records with a photo where the parcel was delivered to.