The CMOS sensor in the GP (the image chip) is rated at 12MP.
The 3.97 lens is rated up to 16MP - meaning it is optically clear enough to handle the finer resolution of UP TO 16MP. For our gopro, it might as well be rated at 12MP. Anything higher than 12MP will work basically the same as if it were 12MP, anything lower and the image quality starts to degrade as the glass isn't clear enough for that resolution.
No matter what glass/lens you put in front of the 12MP sensor, it will still only take 12MP images.
The 3.97 lens is rated up to 16MP - meaning it is optically clear enough to handle the finer resolution of UP TO 16MP. For our gopro, it might as well be rated at 12MP. Anything higher than 12MP will work basically the same as if it were 12MP, anything lower and the image quality starts to degrade as the glass isn't clear enough for that resolution.
No matter what glass/lens you put in front of the 12MP sensor, it will still only take 12MP images.