Al,
I threw that MN11, MN16, MN20 in there as a sort of disclaimer that although they look alike, they might be different. The MN20 is certainly more robust, and needs at least 7.2 volts under load to run at it's best, while the MN16 likes 6.8.
And of course no one with normal facilities can tell if the gas mix is different, or the tungsten composition is unique.
My belief is simply that manufacturers tend to like to standardize as much as possible. Using that reasoning, IF you ALREADY have a very good 3 cell lamp that puts out over 200 lumens, why reinvent the wheel? Surefire is nothing if not a master at making the best out of what is available! When you LOOK at the lamps, and understand that they use the same power supply, and then understand that the outputs are essentially the same, it doesn't take much of a stretch to believe that they are using the same lamp.
This is especially true if you try to optimize costs over lines. The P91 is used in several lights, the MN11/16 in only one. Economy of scale would say, "Use the same lamp in both!" Now Surefire may have decided there were advantages to not doing so, but it seems such a waste!
I can understand that the M3 reflector is optimized to be more effective than the P91 reflector with the lamp, and thus I suspected that was the reason for the higher output numbers, but the lamps, they look the same to me! Obviously, they could be different, and for the reasons you mentioned.
I've asked Surefire CS, but they act like it's some secret, or they tell me they don't know, (which they may not!).
I'll certainly accept your word that they are different. You, at least, are in the place to know!
Bill