Has anyone taken a look at AC's weekly update? What the heck is DE-indexing?

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Okay, so if you looked at ac's weekly update it looks a little bleak. No worry, because if they don't fix there problem soon they won't have a website to worry about. The discussion is still about the fact that the new articles aren't indexing and in fact anything that is searched for will only show up if it is older than 2009. This is so not good. Supposedly they don't know what the problem is. Old timers ready to leave. Anyway, what is DE-indexing? If something is already indexed and able to be found on the search engines, how does it become de-indexed. Does that mean the url has change and therefore it's not indexed? If this is what's happening at AC does that mean they are doing it to themselves?