The 170 sale was outdated when the suggestion was created (which is what technically matters). Of course its good to keep note of all sales within the 3 month period to determine outliers, but given a case like this with two discrepant sales, one being very old and the other being more recent, the recent sale flat will be fine in most cases. If there was an argument that 300 is an outlier, this would have to be left outdated as the alternative, as the 170 is too old to be used in a suggestion.