Comment 3 for bug 713876

All versions of our source packages are available on Launchpad,
distributed by us. True, they aren't on the same server, but we do
distribute them for at least the lifetime required by the GPL - in fact,
I'm not aware that we've ever deleted any library copies of source
packages since we started using Launchpad for our archive.

  https://launchpad.net/ubuntu/+source/PACKAGE-NAME/+publishinghistory

I marked this as Importance: low because it's a CD assembly issue, not a
failure to provide source code (which would certainly be of much higher
importance).

Individual Ubuntu packages are obviously built as you say: source is
uploaded first, then binaries are built from that. However, we do not
rebuild the binaries from source every time we build a CD set - it would
be prohibitively slow. The difference from your analogy with other
shops is that CD images are assembled, not compiled: they're built from
pre-existing binaries taken from the Ubuntu archive. Since different CD
images are built at different times, there's version skew. We have thus
the following choices:

  1) Build individual source images for each binary image.

     This is what we used to do. However, the space cost is prohibitive
     because there's so much duplication, and for the same reason it's
     not convenient for users trying to keep a source archive. We
     therefore switched to ...

  2) Build a single set of source images during the binary image set
     cycle.

     This mostly works, but there's unfortunate skew.

  3) Once we've built binary images, retroactively construct a set of
     source images with the union of all the versions found therein.

     This is probably what we need to do.