I wonder if they really solved the problem with newer units or simply disabled the defective microphone. That is, Lumia 930 has 4 mics, so they could simply apply an alternative wiring so one of the mics responds as the third and fourth mic. I'm still trying to find a way to test the existence of four mics, but I didn't find any app suitable for the task.
Maybe I'll develop a simple app just for capturing and saving a file with 4 channels (or perhaps two files with two channels each), but I'm without time...