Yes, my understanding now is that the rusting is likely caused during the "necking" or "cutting in" process that Sach has described. There was another example discussed
in a message in Dec 2007 - and that amount of rust is quite typical on many of the old "Dump" weights.
My use of the term "pontil mark" is simply to maintain a usage of wording that has become common amongst collectors in most English speaking countries. For correctness, in many (most?) cases of paperweight manufacture, perhaps we ought to speak of "finishing" - which also includes final polishing. "Pontil mark" (or "pontil area" as is sometimes used) is, however, the most widely understood term for the various lumps, bumps, ridges, ground bits, etc. remaining on the central part of a paperweight base.