Hmmm, I noticed that the top 50 for guilds are calculated from historical data rather than the last 30 days, this creates some rather interesting effects.
Case in point, Ancients Ways on Bleeding Hollow was disbanded and the actively raiding members joined Elite Chaos. AW still shows as a top 50 alliance guild but when clicked on you will not get any data for it as there are no active members.
Not a big deal but something to keep in mind if these calculations are revisited.
Hrm... actually what could be happening is that if there are zero characters seen in the last 30 days for a guild, then it doesn't update that guild's value.
