My opinions, mostly in italic:
Scenario One: You're in a bar and Bob says, "Let's go have fun in a different bar." So you "follow Bob", who puts on his disguise (and becomes a shrouded boy) then starts walking down the street. You're a little slow and you lose sight of a shrouded boy in one room, but you quickly catch up to him in the next room(which you know is Bob OOCly). However, he is still disguised, so should you "follow shrouded boy" and assume he is Bob or have you lost sight of him for good?
Because there should also be ambient boys with disguises in each room.
It would depend on the scenario I think. Does the person WANT me to be following them and does my character know that? If so, then I'd probably just continue following them. Otherwise it would probably be safer to just lose them in the crowd.[\i]
This brings me to the second scenario: If you see a shrouded boy in one room, but then they disappear for awhile and you see another shrouded boy in another room near the first room some time later, should you assume they are the same shrouded figure? Because, I know again, ambience should be factored in.
I'm going to replace 'shrouded; with 'disguised' here. And I would say no, not unless they are rocking some very identifiable features like scars or birthmarks or something that your character ca see.[\i]
But it also depends on location. On the streets of the mix, you have a ton of people. On the rooftops, not so much. So if you see the disguised boy on one rooftop then a short while later you see them on another rooftop that can be accessed by the last, then it is probably okay to -suspect- they might be the same boy.[\i]
And how long comes into play. Has it been minutes? Hours? Seconds? t matters![\i]
Scenario Three: SIC yells "Hooded tall boy just killed someone on Bob Street." And you walk over to a Bob street, where you see a hooded tall boy. However, ambience-wise, there should be more than one hooded tall boy in the room. Should you assume that hooded tall boy is the one referred to on SIC or not?
I would say no. I mean, a street is a big thing, event he small ones. And there are corpse in the gutters on most if you read the ambient descriptions that pop up. If it is a small street and the body is fresh and the hooded tall boy is tripping the corpse of gear, then you are probably good. But otherwise, you probably don't know. You really have to consider the situation.[\i]
Scenario Four: You want to kill Bob, an average man. You walk into a bar where you see Bob undisguised, then walk back out and wait outside for him. Soon, a shrouded average man walks out the bar. When ambience is factored in, you've probably seen a few average men in disguises walk out, so should you identify this shrouded average man as Bob or not?
Again, unless Bob is sporting some visible identifying feature that you character knows about and can see, probably not. Could be anyone. But this could go from a probably not to a probably with some help and coordination. Did your chum inside the bar send you a private SIC just as they were leaving and mention the color of the disguise they saw him put on? Then you had a strong reason to suspect the dude.[\i]
As you can see from my responses, I am firmly on the side of applying common sense to the circumstances and erroring on the side of "I Don't know." Every time this has come up with me the GMs are interested in details. Locations, timetables, exactly what was worn, what tools/friends you had to aid you and more. And I can honestly say that I have screwed this up before despite my best efforts.
In the end it comes down to, "Can you make logical argument, from an IC perspective and taking into account ambient population at the location(s) in question, for having IDed that dude?"
