The idea of surface rendezvous for supply missions to a Mars expedition (either before or after arrival of a manned expedition) seems to come up every now and then. This would allow a manned spacecraft to either land near a supply craft, or would allow a supply craft to land near a manned base.
However, that obviously requires close to pinpoint accuracy in landing position. Anything worse than that, and the two spacecraft might be too far away from each other for any supplies to be of significant use.
For our Mars missions of recent past, what has been the landing position error compared to the landing position intended during the final mission planning stage?