Private Thoughts Made Public

Ok I’ve found something work-related to have a rant about.
Why oh why oh why (oh why) can people never follow simple instructions? Without trying to give too much away about where I work, I’ll just say that part of my job involves printing out letters for our customers basically inviting them to come back in to our stores and spend some more money. Each store maintains its own database of customers, and I get a backup of all their data once a fortnight and use it to print off the latest batch of letters. We print a main letter for customers due back in now, and a follow-up letter six weeks later if we still haven’t heard from them.
Of course, over time people move, die and so on, so if a store receives notification that we’re not to write to someone again, they should edit the customer record and replace the first line of the address with a row of X’s.
After that, any customer with an address that starts with “XX” won’t get another letter. Grieving widows are left to their grief, new householders aren’t pestered with mail for people that don’t live there any more, our data gets a bit more up to date and everyone’s happy.
So how come when I print a second letter a few weeks later I have to sort them out and remove all the ones addressed to Mr Smith at ********** or X XXXX XXXXX or 22 XXXXX or ++++++++++ or any other combination of incomplete addresses?
Surely it’s not that complicated, is it? Or am I living in la-la land expecting people to understand “replace the address with rows of X’s”?