There will be more than 1 letter, they are sending 2 letters.
The practices are overworked as it is, they will not have time for the receptionists to go through all the records - this is something that can only practicably be done by a sub contracting outside body.
How else, if not 2 letters should they identify people? perhaps you would like them to go visit each patient on the list?
Neil has pointed out the flaws in the new practice listing, which if someone had registered at a new practice, they would then be able to point this out to the old one when they send them a letter!
Margaret, you seem to just complain against anything and everything - next the knives and forks will be out to get you!