"We investigate the issue of coordinate stability over time and show that coordinates drift away from their initial values with time, so that 25% of node coordinates become inaccurate by more than 33 ms after one week. However, daily re-computations make 75% of the coordinates stay within 6 ms of their initial values."

That's the intro from a 2007 paper from Google:

https://static.googleusercontent.com/media/research.google.c...