philkool I soooo wonder the same thing, mine is 4 years now and after her mot in november I noticed a small lump on her back, she was chipped as a kitten and I'v never noticed till now.
The chips are inserted between the shoulder blades at the base of the neck, but they can move. One of my dogs has got one just above her elbow (I put it in myself so know it was put in between the shoulder blades).
one of our dogs has a shifted chip. It was put in between the shoulder blades, I was holding the pup at the time and saw it done, but by the time he was 6 months old it had moved to the point of his scapula where it remains.