Just more of your total nonsense. There's no way for spores to get through a plastic garbage bag. If a plastic bag can hold water, it can contain spores.
When the letters found, they were put into plastic bags for moving from the scene of the crime to the laboratories, and from one laboratory to another. They are probably inside plastic bags right now.
The idea that spores can get through plastic bags is laughably ridiculous.
Office workers don't seal water-tight plastic garbage bags of discarded mail.
The sheer act of hand-closing a plastic garbage bag will force out anthrax spores as if blown out onto the garbage pail from a bellows. This in turn contaminated the exterior of the garbage bag. That in turn contaminated each garbage bin that the bag goes in to, and in turn the bag contaminated each garbage truck.
No such garbage pails and garbage trucks servicing AMI were contaminated with anthrax, however, rendering your "oh, we just can't find an anthrax letter because it was thrown away" theory obsolete.