We must bear in mind that our knowledge of the universe is progressive. Figures changes (or should we say IMPROVES) as we learn more with new technologies.
We need not quote 'the number of stars in our MilkyWay", or the "distance of M31" as these number changes as we have better technology to enable us to reach better (still not ACCURATE!) figure. Just look at our neighbors: Jupiter and Saturn - their number of satellites have been increasing by the month, then we have the 4th moon of Pluto. All these are results of our much improved technology.