Every printer in America? She wasn't a random person accessing those documents in her local Starbucks. That was a secret document printed in a government computer.

It's cheaper and easier to look at the print logs. Most business computer and printer solutions tie every print to a user and log at least the name of every document printed

The hidden code is for court cases where they wish to prove which machine made the print, they're not very good for identifying which user printed something in a multi user environment