source of packages in d-l package lists

[jpryzby+d at quoininc.com (Justin Pryzby)]

What is the derivation of the packages in the d-l package lists?  How
about the packages which aren't in any debian suite (say, nxagent)?

grep -h '^[^#]' /usr/share/live-helper/lists/* |grep -Fvwf <(apt-cache pkgnames)

(Yes, that's a bashism).

Thanks
Justin