I must be something attached post-harvest. Is there a photo direct on the "hairy blemish"? I see no cracking of the nacre from the angle yet there are multiple protrusions. The pearl is strung in a strand and nothing is going to grow post-culturing, post-harvest and post-processing on a nucleus.
I have never, ever seen anything like this on a pearl before. My guess is that it is not actually coming through the nacre. Somehow a small particle of epoxy was smudged on the pearl and the strand was placed in a box; a black box. The owner should take a chance on the pearl and scrape!
Five o'clock shadow ...
Is that you, GemGeek?!