A yellow slip pops up with the new address (a lim lim) and its pasted on the letter (at that time, BTW, and this system is always changing).
Mistakes are made ~ AMI for AIM seems perfectly reasonable to expect as an error.
Only if you ignore all other facts.
You have to ignore the FACT that four other letters were mailed at the same time, and ALL went to media outlets.
You have to ignore the FACT that the trail of anthrax through the post offices indicates that the letter first went to Lantana where The National Enquirer was previously located.
You have to ignore the FACT that the letter was almost certainly opened by Stephanie Dailey whose job was to open letters addressed to The National Enquirer.
You have to ignore the FACT that if the letter was addressed to AIM instead of The National Enquirer, it would almost certainly have been returned to the Post Office instead of being opened by Stephanie Dailey.
You cannot simply say it could have been addressed to AIM instead of AMI without looking at ALL the facts. Maybe it is still possible, but it is so unlikely that it is in the range between preposterous and ridiculous.