You're getting your poisons mixed up.

Tabun is the first nerve agent that went into production in 1939. The Germans didn't start sarin production until 1944, and only a small amount was weaponized before the end of the war. Sarin is about twice as effective as tabun, but not as persistant.
Now to the antrax: Antrax has been used as a biological weapon since ancient times to kill livestock and horses, and is described to have killed 40,000 horses and 100,000 cattle in the possession of the Huns during their movement across Eurasia in 80 AD. Antrax wasn't properly weaponized for use against humans during WWII. The 1944 British project was aimed at Germany's livestock, not people. Infected cow patties are not going to infect many people, or start an epidemic.
When Antrax was weaponized in the late 1950s or early 60s they found that gas masks or even just breathing through a damp cloth will protect a person from an anthrax attack. However, anthrax is extremely persistent and would cause random cases of the illness, perhaps even small outbreaks for decades after an attack. Antrax is deadly against an unprepared population and thus perfect as a terror weapon, but as a weapon of war it is very limited in its usefulness.
HOW TO WEAPONIZE ANTHRAX: (This is not a secret, it was printed in TIME)
1 DRY THE SPORES
If they are grown on a culture medium, anthrax spores need to be dried. Because they are so durable, they can be freeze dried, heat dried or spray dried
2 MILL THE SPORES
Once the spores are dry, they are ground down to the smallest possible particle size, anywhere from one micron (one spore) to 20 microns. The process adds electrostatic charges to the particles, which makes them clump together
3 NEUTRALIZE THE SPORES
Chemicals such as bentonite or silica are added to remove the electrostatic charge and allow the tiny particles to float in the air
...AND HOW IT DOES ITS DEADLY WORK
In order to cause disease, at least 8,000 to 10,000 spores need to lodge deep in the lungs, in the tiniest air sacs known as alveoli. The warm, moist environment, and possibly the concentration of carbon dioxide in the lungs, stimulates the bacterium to emerge from its protective spore. As each bacterium reproduces, it releases toxins, which eventually spread throughout the body and destroy tissue and organs.
Oh, and a blunder...."less than 20% of the known victims died" (mustard gas) and "If it had been tabun, the number of victims would have been 100-fold".
I presume you mean (as in the end of the sentence) "the death ratio would have been close to 100%." I would not doubt that, since the Tabun is very...something...nasty.
I meant that instead of 600 known victims there would be 60,000 victims (100-fold), and instead of 80 dead it would be close to 60,000 dead (close to 100%). They could treat mustard gas poisoning and managed to save 80% of the exposed. They couldn't have treated tabun poisoning.