Comment 24 for bug 191327

David,

you can only ever have one version (what you call "unique identifier") of a package installed. What you see in /var/cache/apt/archives is just a temporary download place where apt and other package tools download packages to before they get installed. This directory generally has multiple versions of a package (you can use "apt-get autoclean" to get rid of older ones and free some space).

Uninstalling a package with "apt-get remove" does not remove the downloaded .deb package from the cache.