Even assuming they had vaccinations and prophylactic antibiotics (and that is a fair assumption) every precaution would have been taken.
I think the envelopes were filled in the lab where the spores were produced. There was no charge on the spores, so the question in my mind is not where the envelopes were filled, but how the perps managed to get these spores into the envelopes. Some kind of negative pressure system and a glove-box would be needed, at the least.
It is absurd to think someone could fill paper envelopes with *this* anthrax outside a lab where conditions are not predictable or under control.
If, as I believe,
the donor wanted complete control
over how the anthrax was used,
then 'he' agreed
to have the addressed envelopes filled
in the place where the anthrax was made.
I do not believe
'he' was willing to send off supplies
of raw 'Daschle-grade' anthrax
either to terrorists
to use at their discretion
or even 'agents',
(whoever these mysterious people might be,
somehow loosely connected to Al Qaeda
but exercising control over them)
Thus it may be
that there is no 'stash'
of raw Daschle-grade anthrax
in the USA......yet.
(Some of the lower grade Boca Raton stuff
may be 'floating around' however.)