I've read that when bones have given up all their nutrients they go soft. I tried simmering some cow bones, with vinegar, for over two weeks (perpetual broth style), but they're still not soft. Should I just keep simmering them forever?
I'm surprised that they're still hard after 2 weeks! Are you removing the broth and adding new water? If not, you may just be reaching a chemical equilibrium with the nutrients in the broth and the bone (I don't know that this has ever been studied!)
If you've been replacing the water then I'm really surprised! Those are some crazy bones you have! lol!
Here's a link about making bone broth for 12 days (not a paleo site): http://www.traditional-foods.com/bone-broth/