The 50 weekly agreements for the past week would be dependent on Niantic and when the portals are rated. That's going to mean you probably have to vote on at least 100 to have a safety net for the weekly stat.
Yeah, I haven’t reviewed as much as I normally do this week and I am on 49. (Not that I am attending this)
More notice would be great for this in future if you want to get into the swing of doing more reviews.