Thanks. It is clear from this that "Rsync Mirrors" is not at all what
I thought it was. I had thought it was an improvement on jigdo for
downloading an updated version of an iso for which I already had an
older, out-of-date file.
What I had thought was that I could take my netinst.iso from a few
months before Lenny release and rsync it into being a true copy of the
latest version of Lenny netinst without having to transfer ALL the
individual bits of the new copy. That would save some time and
bandwidth over downloading a whole new copy, but ... I sure was
mistaken. I certainly don't want to mirror the whole Lenny repository
locally. No wonder Thorny was puzzled by my question!