Scarce Songs and the broadside ballad index are the ones most often updated (more typo and other corrections than additions) I try to keep revision date at the top of the files so you can see if there's anything new since the version you last looked at, but there's enough involved in checking out how the texts in Scarce Songs look and whether I've gotten the links from the index right, that I've heaved a sigh of relief at that point, and then forgotten to change the revision date.

Every 3 month is probably too often as far as anything really new is concerned, but I try to be as accurate as possible on any reference data, so corrections to that I do immediately, and for the broadside ballad index there have been as many as two updates in one day.