I don't know when the one trillion spores per gram was perfected. I hadn't heard of it until the mail incidents. If you have information as to when it was perfected I would certainly apreciate you sharing it.
In the meantime, consider the following.
According to the BIOHAZARD NEWS publication, "a 1997 article in a scientific journal reported that Russian scientists had implanted into the anthrax microbe genes that cause food poisoning, producing a strain that was resistant to Russia's anthrax vaccine." (Could Alibek have planted the story?)
At any rate, U.S. authorities requested a sample from Russia with which to test the U.S. vaccine but were unsuccessful when Russia denied ever having produced such a strain.
Thus was born the "Jefferson Project." The CIA was tasked with developing more deadly anthrax bacteria to use in testing U.S. vaccines. The CIA chose its often used contractor Battelle (BMI) to host the project.
Production was to be at Battelle’s state of the art facility for making aerosol products for commercial and military use. Some researchers believe this may be the facility at which William Patrick perfected the process that resulted in the one trillion-spore concentration rather than at the army’s Dugway, Utah facility, which is also controlled by Battelle.
The aerosol facility is located in West Jefferson, Ohio hence the name of the project. No results of the project have been announced.
...In his report, Mr. Patrick said the American program had achieved a concentration of one trillion spores per gram — what scientists today say is near the theoretical limit of how many of the microscopic spheres can be packed into a tiny space.
New York Times12/3/01 - William Broad "Terror Anthrax Linked to Type Made by U.S."