The Chinese stealth ships never got close enough to attach a tracking device, as if they did, sensors would have picked them up. Also, in a fit of paranoia, after every jump The Japanese Republic clean off all foreign matter after every jump. This happens to include every tracking device they find, which they then launch in a random direction. This is done so many times, all of your stealth ships tracking devices are used up and lost. The Japanese Republic continues jumping around the known and unknown galaxy, completely losing your stealth ships yet again.