It was my understanding that it had to do with the size that the NC board started to become, so it was split on a logical line that exists within the other boards. I could be wrong on that, though.
I freely admit that I'm something of a curmudgeon (most of you active in this thread have probably heard me say so before!), but I genuinely think that a single chart, or, as Caeli has said, more prominent use of existing descriptions should be fine. If people ask or complain or anything, have a boilerplate answer available to send them, or just give them a link to the chart. Send the chart to every new member upon approval.
I think the reason why we have each split relates directly to major areas where there are divisions of psychological comfort, and I believe that, on a board this size, the separation makes more sense than does tagging.
Explanations that are readily available will be read by 'good citizens' and can be pointed out to those who don't bother to look by 'good citizens' who have. Those explanations make more sense than reorganization, IMSNHO, but I'm just me and kinda cranky tonight.