I will take a guess here that you are referring to this chart by ZWO when you say the camera is only 11 bits at a gain of 139 and 12 bits at a gain of 50
This is actually referring to dynamic range in the language normally set aside for those ancient cameras that used film. In this instance a dynamic range in “stops” simply gives you an indication of the difference between the brightest and the darkest parts of the image it can record. It has nothing to do with bits or bit depth. It is also a relative measure that allows you to compare different camera settings, so all you can tell from this is that with Gain=139 the number is 11.1 stops and at Gain=50 the number is 12 stops. Therefore at Gain=50 the camera will record just under twice the range of dark to light (each stop is double).
We can actually calculate what it really is from the other charts such as the full well depth chart
This tells us that the electrons are 11.4k and 4.1k for the 50 and 139 cases. This means that the true dynamic range difference between these settings is 2.79, or almost 1.4 stops, not just under 1.