One trouble is that (for an example from the paper) two trees growing on the same hillside but different elevations generally have quite different and unmatchable tree ring sequences, even when they are contemporaneous. There are also problems with soils, such that volcanic soils are enriched in C12, leading to plants showing false antiquity.
Probably so. I find the tree-ring patterns in the spruce I cut from my own yard to be hard to match when the trees are only a few yards apart.