Just a bit of clarification here, as far as I understand it: the one's marked with an 'x' are those that steamspy's system picks up as having lots of variation in the data, suggesting there might be a factor like a free weekend screwing with the numbers. The majority of games in the list marked as such haven't actually had a free weekend, and therefore should be accurate (e.g. Counter Strike:Source). However, there's also some games that have had semi-recent free weekends and which aren't marked as suspicious, such as Company of Heroes 2 and Rome 2.