This is as far as my understanding when it comes to tracking wooden coasters so take it with a grain of salt.
Wood coaster track pieces are not shaped when they are added, for example they don't take a piece of wood and then cut it into a 180 degree arch and then lay that on the bents. (that would be a huge waste!), they take normal 2X4's (I think) lay them out flat, and then cut the excess off. Many times these pieces will be laid at a diaginal, especially on curves. If it makes it easier I will use an example.
If laying wooden coaster track was like making a 3-layer round cake. What the construction works are doing is making 3 square cakes, laying them on top of each other, and then cutting around the edges to make it round.
BTW you certainly in the best of circumstances wouldn't want them to only replace two layers (obviously if that's the only option its better then nothing), you would want them to replace as many layers as possible. I believe T-wolf was built with 8 layers of track, and then when it was re-tracked that was expanded up to 11-12 layers (someone correct me if I am wrong). The more track that is replaced the longer the track re-tracking job will last, and the longer the coaster will remain smooth.
Jennifer