Finally got around to getting the Famine Skull (only five years late, right?), which is all thirteen skulls for me. The Hayabusa helmet didn’t unlock, which as I understand it, it should have. I already have all the other pieces. It might be worth mentioning that I haven’t unlocked anything since 343i took over the online aspect and gave everyone Recon.
It’s not a personally pressing issue, given that I probably won’t wear it anyway, but it’s troublesome all the same. More than likely it has nothing to do with the aforementioned 343i coup (bloodless; all smothering) and it’s just some stupid glitch. But if anyone’s had similar experience and/or found a fix, it’d be great to know.