2004.03.10 2.31984 ± 0.057045 2004.06.10 2.53101 ± 0.259411 2005.05.18 2.28919 ± 0.093442The June '04 data is noisier for some reason, and some of the data points don't seem to fall on the expected linear relationship between mean and variance; if I throw those files out, I can get a gain of 2.28 ± 0.10, which is more in line with the March 04 and May 05 data.
So empirically, it seems like the Kermit gain really is around 2.3 e-/DN ± 0.1.