Do we know which are unused?
As far as I know, most of the contrib/req fields are either a) evaluated by the Vell-os string to see if you actually have a non-vell-os ship or b ) linked to Fed licenses. That would mean that A1 B1 C1 D1 G1 and H1 are all taken, as is A5. Is this correct, or are there other fields that are used? (I'd really rather avoid going through every mďsn, oütf, crön, and shďp if possible wretches).
I ask because I'm adding an outfit that "hardens" titanium lattice that can only be applied once per application of titanium. What it does is when you buy the hardening, it replaces the standard titanium oütf with an identical outfit with twice the armor value via the dxxx command. Now, in order to ensure that one can only harden their titanium if they have some in the first place, you would need a contribute/require field. As far as I know, NCBs won't work because you can have a total of 3 titanium lattices at once, so even if you had buying a lattice set, say, bit 1 and toggle bit 2, the coding would only be reliable if the character only bought 2 lattices. And you'd also have to set every ship in the game to clear bit said bit 1 on retire, which is a major hassle.
One other (and probably stupid) solution I thought of was making a titanium wëap turreted beam with no stats and 360° blind spot with a MaxAmmo field of 1, then making link the Titanium Lattice outfit to it and make the reinforcement it's corresponding ammo. With this system, the hardening outfit would just add another 110 (the base value of Titanium Lattice) instead of replacing it. I have no idea if this works at all, and even if it does it's a very crude solution, but hey, it's kinda fun to tinker with the mechanics like this. 