Your in NYC, they write their own Code's. So my answer might be worth nothing!
The underlying answer is that the UL has and approved various wall assembly's to get
the required rating of various gypsum usage's and insulation. It's approved as a "package" and if you insert something in there you'll going to isolate any fault to the outside face of the wall.
Now I believe per the IBC which most other regions work from. It doesn't matter what's in a Fire Wall, it gets puddy pads. In most cases your not allowed to be with-in 24" of each other period. As I recall.
As I learned it, Fire walls with a break in the wall with use such as a device box, one is isolating the box with puddy pads to the open face of the wall and isolating the device box from the cavity of the wall. Is doesn't matter about the rock wool is there, for example it could be three layer on two sides with no insulation.