2.5 Why does the official stable released CD-ROM contain symlinks for `frozen' and `unstable'? I thought this CD contains just `stable'!

Official Debian CD images indeed contain symlinks like:

      /dists/frozen -> sarge/
      /dists/stable -> sarge/
      /dists/testing -> sarge/
      /dists/unstable -> sarge/

so that they work when your sources.list has an entry like

      deb cdrom:[<name as on cd label>]/ unstable main [...]

.

The fact these symlinks are present does not mean the image is `unstable' or `testing' or anything. Read the CD label in /.disk/info to find out which Debian version it contains. This information is also present in /README.txt on the CD.

Read https://www.debian.org/releases/ to find out what the current `stable' and `testing' releases are.