It is important to understand that these notices must be rather simplistic and do not necessarily reflect the actual cabling.
Post codes were not invented for BT and you will find many that span 2 PCPs.
Friday afternoons happen frequently so you may find a few lines allocated to say GU1 1ZZ which, as you have guessed, does not exist.
Furthermore the post codes can be (infrequently) changed but it does not seem to trigger a re-work of that section of the database upon all occasions.
In our area I know of one cabinet which ran out of E side pairs so there is a tie cable to another PCP that presumably had more spares available.
The very least this means is that a single PCP can also act as a SCP for those circuits connected via the tie cable.
Obviously if there is a choice of FTTC the SCP one would be better as it reduces the total D side length.
It is also not unknown for BT records to be inaccurate and in some cases non-existent, but I suspect many of those are in remote areas without any chance of FTTC anyway.
Kind regards,
Walter