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That's a great question...I actually just rely on a trusty old spreadsheet like you've been using. I never delete ads or keywords unless they are super old. I will do an export after pausing a lot of ads/keywords and make sure I put notes next to each ad/keyword to say why I paused it. Then whenever I do keyword expansion or ad optimization, I reference this sheet and perform a "remove duplicates" search before uploading any new keywords. Would be great if there was a plugin of some sort out there but I just don't know of any off the top of my head. If you find one, let me know. Thanks! -Justin