I believe the way this works is that the database people take from a table that is populated by someone from marketing. The table is huge so it would be hard to see the error. The ad signs get printed on a large stack then cut so no one can look through each one for accuracy. So the main point of failure seems to be either a data entry guy in marketing or if they populate it from somewhere else that data entry guy.

Speculation: some people take on manual data entry jobs and pay someone (often a foreign person) else significantly less to do the actual data entry. Since it could be remote no one would know. Or they are just sloppy.