For the two Lovenox patents originally in play in the patent-infringement suit against Amphastar, the duration of prosecution by the USPTO varied a lot: 2.7 years for the ‘466 and 6.5 years for the ‘886. Based on your table, the ‘886 was the outlier.
“The efficient-market hypothesis may be the foremost piece of B.S. ever promulgated in any area of human knowledge!”