As you must realize you do not have to be in a jurisdiction to put it down as a return address.
The thing the FBI was confused about were the cancellation marks. They are in New Jersey.
All that meant was that the pieces were cancelled in Jersey and not Florida. That's because they got were lost in the mail in Florida, yet discovered in flat trays in New Jersey, and tossed into 010!
This is a normal situation. Happens all the time. It's happening as we speak!
The window drop at Boca Raton was contaminated. I am certain a half dozen or more flat trays were also contaminated. In later handling those very same trays which were contaminated with anthrax went on to contaminate other mail destined for folks in New York and Connecticut. Two of them died.
It was not cross-contamination from mail - it was contamination by contaminated equipment!
I am taking a break for a while to watch Indiana University kick Kent State out of the arena!