Recently, I had a colleague refer to GPO as the Government Publishing Office, and my internal dialogue sounded a red flag. I had always known it to be the Government Printing Office. So I looked into it.
The Wikipedia entry states, "[i]n December 2014 an omnibus spending bill funding US federal government operations was passed which included a provision changing the name from "Government Printing Office" to Government Publishing Office. Following signature by the President the change took effect on December 17, 2014."
Than you Wikipedia! It can be difficult to stay on top of these subtle changes, and Wikipedia makes it that much easier.