Another thing to consider is that the official AT route will change over the period of years a section hiker will take to do the trail. I noticed a prior poster mentioned that he wanted to hike every inch of the AT, that can be an issue for section hikers as the official AT route changes from year to year for short term issues like severe weather events or longer term events, like bridge construction or just plain relocations. In theory hiking every inch would over a multiyear period means having to go back to pick up these points. As an extreme example, in 2011 after Hurricane Irene came through Northern New England in August (prime NOBO season), the entire AT was closed from the Mass/VT line to the Whites for several weeks due to severe erosion and blow downs. During that time there was no continuous AT route from Me to Ga and no official blue blaze route. Per ATC guidance at the time thru hikers could legitimately skip this section and still be a thruhiker. Given the distance some official AT thruhikers were not 2000 milers. Some hitched around, some yellow blazed the stretch (a dangerous effort in some areas) and some tried to follow the closed route. Using a less extreme example there have been a couple of major detours for bridge reconstruction, usually a road walk or on occasion switching to another blue blaze trail. These could be as much as 10 or 12 miles off the usually official AT route. Per ATC, the blue blaze is officially the route during the time that the relocation is in place but how would a section hiker doing multiyear effort treat this gap?. To me the rational method is to hike the official route as it exists during the period of time you are on that particular section of trail but some folks might have to go redo it once it reopens. The other official reason that ATC allows a gap is when the conditions are too dangerous in the short term to follow the AT route. They don't define dangerous but a good example is severe thunderstorms on an exposed ridge. I did a blue blaze around the Priest in VA one year as the conditions were dangerous in our estimation, temps in the 20s, ice, high winds and snow in April. I did pick it up a few year later but I would have considered the blue blaze legit the first time around.

I must admit we did do a "victory lap" down south the year after we finished the AT to pick up a few sections we missed that we had to blue blaze when we originally went through the area. It was mostly a way to leave late winter behind then being anal about white blazes.

One of the things living up north near the AT and having contact with thru hikers is the change in perspective compared to my interactions with thruhikers down south. Sure I have met a few very rare individuals still on the "walk past every white blaze" concept but far fewer than down south. One thru hiker in Maine observed, folks with rigid rules like that were the ones that dropped off the trail. It may be just that down south, the individuals who were on that kick had to tell everyone they met to convince the selves it was worth doing while those up north were self confident and didn't need to announce their intent.