I'm not even sure if GRP (Gentoo Reference Platform) is supported anymore. But the Handbook links to the "Gentoo 2008.0 Networkless Handbook" for doing networkless and GRP installs. However every page in the "Networkless Hanbook" has a box at the top saying: "Disclaimer : This handbook has been replaced by a newer version and is not maintained anymore." The question is where is the newer version? The recent regular Handbook is linking to the "older" version. Or if it's the case that GRP is not supported anymore, perhaps the handbook should no longer reference it.
You're right; referring to a 5-year old installation isn't practical anymore. I've removed the references to GRP and the 2008.0 instructions from the first chapter.