In the Stargate universe DHD and the computer system used by SG command can 'fine tune' the gate address and make sure despite the gates relative positions changing (due to, as Jeff points out Stellar drift), that they can lock on.
Here is an image of the dialing system/co-ordinates
To my knowledge, the far blue points are fixed by the chevrons. If the chevrons are wrong there should be nothing you can do. Also I was under the impression only the the chevrons in on the gate determined the location the gate went to. So how do you fine tune a stargate, when you only have chevrons to adjust, if they can be adjusted?