A few things....bit depth (8, 12, 14) does not define dynamic range, nor does it define potential dynamic range. All bit depth does is determine the number of slices in the DR pie.
The sensor's output to the A/D converter defines the DR.
For example, if camera (A) provides 12 bits of data per channel, and camera ( provides 16 bits per channel, does that necessarily mean that camera ( provides wider DR? No! It could be, that the camera provide less bit depth procides the wider DR!
All bit depth does is define the graduation of the analog data converted to digital. So for example of camera (A) provides 7 stops of DR and 12 bits/channel, and camera ( provides 7 stops of DR and 14 bits/channel, then they both provide the exact same DR, but what is different between them? The number of graduations of tone is the difference. One camera provides more tonal values then the other.
Furthermore, it would be wrong to suggest that one will not be able to see differences in an image that is 12 bits/channel versus an image that provides 14. This may well be true for small prints (assuming the printer can support 14/channel), but as one enlarges a print, one will see more and more the differences, for example in sky tones, graduations from one shade of blue to another, and human skin, and any element of a composition that shows subtle graduations. In other words, more bits is a good thing; a big deal, even if our human eyes will not be able to tell the differences between tone X and tone X + 1. More bits means smoother transitions, graduations in color, and that, we often can see.
The other wonderful thing about more bit depth is rounding errors. For example, if you tweek an 8 bit image in PhotoShop, you're more likely to get combing of tones, especially toward the left of the histogram, the shadows. This is because the math used to apply levels, curves, and the like results in rounding errors, and as you go up in bit depth, you will go down in rounding errors, or in otherwords, result in less digital artifacts such as combing, blocked up shadows, etc.