The GSA does not maintain public archives indefinitely. If you change computers and lose your PDF, retrieving it from GSA can take 6-8 weeks.
GSA no longer mails physical CDs or books. The Good News: It is available instantly via GSA eMod (eOffer/eMod system). gsa noa book pdf
The Role of GSA and NOA Resources in Competitive Examination Success The GSA does not maintain public archives indefinitely