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A similar question was asked last month that might give you some insight as well. http://moz.com/community/q/should-i-use-my-competitor-s-name-in-my-content-to-help-my-rankings

Hey Walker! I can definitely see how helpful specifying date ranges would benefit you and everyone else with a long history. This would definitely be a great feature request which you can submit your suggestion here: https://seomoz.zendesk.com/forums/293194-SEOmoz-PRO-Feature-Requests\ You can vote for features you'd like to see and suggest your own, both of which help our product team in deciding what to build next! Hope that helps!

You've got the right approach there. We do our best to look at the web like Google does, but we don't have quite the resources they do. We do have to make tradeoffs between getting an index out in a more timely manner and getting one out that has a lot of data. The bigger we go, the more problems we run in to. This last index was about half the size of the previous index, which would account for much of that drop. So sorry to scare you!

It's not instantaneous, but yes, you should see that number drop over time.