Don't retap. Those who tell you to tap on the south side, or over a big root, or under a big limb have no real idea what they are saying. The way I always instructed my tappers on areas that were not tapped before, is to tap whatever face you approach the tree from. Basically as long as you are tapping hundreds or thousands, you will end up having taps on all directions as you work thru the sugarbush. Then on gravity you should move over about 3" and up or down 6" the next year. On vacuum it's different, in yr 2 try to tap opposite where yr one was, then in yr 3 tap half way between the first two year's tap holes and yr 4, opposite yr 3. From there you start between the 2 oldest holes and keep doing that pattern. Realize that you can also, on vacuum tap below the mainline and use a similar pattern. By the time you go all around the tree 2 times, new wood will have grown over the oldest holes and start over again.
If you favored the south, it would soon use up all tapping space.