https://bugs.debian.org/933728

E.g.
after using jigdo-lite with http://archive.debian.org/debian/
to attempt to create any of these files:
debian-30r0-i386-binary-1.iso
debian-30r0-i386-binary-1_NONUS.iso
debian-30r0-i386-binary-2.iso
debian-30r0-i386-binary-3.iso
debian-30r0-i386-binary-4.iso
debian-30r0-i386-binary-5.iso
debian-30r0-i386-binary-6.iso
debian-30r0-i386-binary-7.iso
and ending up incomplete due to missing files, then repeat, with:
http://old-debian.balug.org/jigdo-area/3.0_r0/snapshot/
to obtain the missing files.
Note that the above may contain only the missing files.