Let's say there are two observers A and C. C is moving .5c with respect to A. If we introduce a third observer which we will call B and B is moving at .2c with respect to A and is moving in the same direction as C and is inbetween A and C, and we now apply the velocity addition formula we get that C is now moving at (.5/1.06) or .47c relative to A. So, does this mean that without B, C is moving at .5c relative to A and that with B, C is moving at .47 relative to A? Does just the mere presence of B change the velocity of C with respect to A? What am I missing?