The story confuses "bullet" (the projectile), "case" (the brass cylinder containing the powder, primer, and projectile), and "cartridge" (which generally refers to a complete loaded round of ammunition, unfired).
You can't really microstamp a bullet because (a) it never contacts the firing pin; and (b) it is generally badly damaged upon impact.
Never mind that any microstamp will be quickly eroded by friction, and that replacing a firing pin is a matter of minutes with the proper tools.
There have been suggestions in the past that each bullet needs to have a serial number or lot number etched on its base at the factory.