If we're still open for a bit of discussion, I'm potentially having a bit of trouble illustrating UA's and Inhibitors. I have some notions, but I'm not sure if my interpretations are accurate or if I'm stretching.
MC Unique Ability: Perrmission
I think this is the one I'm having the most trouble with. What I'm thinking is that it has something to do with Watson owning a gun (amusingly an actual Chechov's gun). It's hard to imagine another way in which Watson could have stopped the Cabbie in that climactic moment. I'm thinking that because gun control laws are so strict in London Watson having a gun at all relates to Permission: either he owns the gun legally, with permission, or he's in possession of it illegally, demonstrating a willingness to overlook what is permissible. I'm not sure, but I imagine to a British audience Watson owning a gun would be notable.
MC Critical Flaw: Preconditions
Assuming this is a valid interpretation, this must be the shaking hands. They'd specifically prevent Watson from making the shot, and it's a condition he has imposed on himself, even if subconsciously. One of the listed synonyms is "limiting parameters," so I think this works pretty well.
IC Unique Ability: Prerequisites
Is this whenever Sherlock is listing off the chain of reasoning for any of his impressive conclusions? Watson is always really impressed. i can sort of see an interpretation where Sherlock is listing off all the prerequisites that led him to this conclusion. It's maybe a bit of a stretch.
I suppose it could also be that Watson and Sherlock each need a flatmate to stay in London. Sherlock needs an assistant, so he invites Watson along. He needs someone to talk to so he invites Watson to the restaurant. All these things Sherlock needs keep Watson around.
IC Critical Flaw: Deficiency
This one actually seems pretty clear. Sherlock is lacking in pretty much every social grace imaginable. this has severely limited his influence on other characters, but fortunately Watson is able to look past it.
That sounds good.