Being new to the toolbox, I can't help noticing that apparently some work is spent on raising old dust. Lately I've seen migrations of posts from 2009 (1, 2) to SuperUser despite of the apparent consensus that legacy posts are not to be migrated.

Although I am all in favor of the "rules are there so you think before you break them" philosophy, I fail to see a straight line here. From what I have read on meta so far, I understand the guiding principle to be not to touch old questions for migration if they have been answered here. Am I mistaken? Are there somewhat more concise guidelines or is it something to be decided "with the gut" and mainly done whenever one stumbles over off-topic posts?