perhaps you misunderstood me...the quickness of which I was referring to was the idea that Tuesdays mailings were "Hoax copycats" and that was the impossibility I was referring to. Anyone who received a white powder on Tuesday would almost have to expect that it came from the same group as the anthrax. The white powder didnt become public until late Monday. Anything after this could be copycats or the like...and I think the terrorists would be counting on that.
We're on the same page. I still think copycats mailing locally could have responded monday night and, with a little post office luck, gotten their stuff delivered tuesday afternoon. That's what happened when I sent out wedding invitations, dropped them in the corner box around 7:45 AM, went about my normal life, swung by a friend's house about 3 that afternoon and they handed me their RSVP, the mailed RSVPs started arriving at my house the next day with a big bunch on invite day +2. Really it all depends on the postmarks. If the "safe" ones that arrived tuesday were postmarked ANYWHERE other than the city they were delivered in, you're right they were part of the real attack; if the postmarks were in the "target" city probably a copy cat hoax (can't entirely rule out a rather large org sending everything locally). Of course the FBI is never going to let us see those postmarks so this can never go beyond conjecture.
The biggest thing to me that indicates that, at least the main attack, is from a sizable organization is that they had anthrax in the first place. Admittedly it's a naturally occuring thing (haven't seen any indications that either found strain was "weaponized"), but you gotta scoop a lot of poop to find it in the wild (or however it get's out of the animals). So either it was stolen from a lab (not easy), purchased on the black market (expensive), or they had a lot of people collecting goat crap looking for the magical spores (talk about a thankless job, if you're the lucky winner it could kill you). The mailing will only indicate the size of the organization through the postmarks, which will give not only location but date and time which will help with the incredible timing vs really fast post office vs knew to send fakes when first announcement came discussion.