Oh. In that case. The answer is simple. Media
In general, when someone is more confident about what they are saying compared to everyone out there who does not speak a word, you are more likely to feel convinced if you are unsure of it yourself. (I won't go into depth about people who purposely rebel this sort of conformity, but you get the sequence). I bet someone out there could make a convincing argument to suggest that these celebrities do not in fact dress similar. (Sort of like when media flashes ugly trends in your face and you
know you don't dig it, vs. a trend you don't really feel strongly about that everyone is seemingly committing to.)
Lets use animation as an example (given yours). Japanese anime is a great example. Many characters have different identities yet appear nearly identical. They dress similarly, act similarly ... but somehow have distinguishable features which separate them from each other. It may be their voice, the world that they're in, their name, their past. etc Ultimately, I reckon how people perceive you depends on how much they 'know' about you.
I think I sort of see what you're trying to say with one-many, many-one. I guess in those words you've chosen, 'trademark identity' uses the one-many concept (you create it for yousrelf) and 'distinctive style' uses the many-one concept (the public creates it for you).
I personally don't think how people perceive celebrities is entirely dependant on their appearance so much as their public image and what is already published about them. Unlike celebrities though, people walking on the street may not have that sort of 'tabloid history' you can refer back to...so everything you see in front of you formulates your entire opinion of them in that split second. As such, I do think first impressions in 'appearance' play a fat role in determining how you get perceived.
Lets use the 'happy goth' example. If you were to take identical twins and put them in a small sl*tty black dress, you'd logically get seemingly clones. Now, if one were to have a sunny disposition (lets just say, Hilary Duff) and the other one had a more less-sunny disposition (lets say, Lindsay Lohan)... the difference in personality would generally affect how you perceive the type of person each of them are despite the identical clothes they're wearing.
When you think of celebrities, you're comparing personalities a lot more than you're comparing your first impression of a person walking on the street. The reason is because you 'know' more about them (I think anyway) and can attribute factors to accommodate what you're seeing. So the difference in one's physical appearance is proportionate to the perception of who they are and how much you know about them already.
Take another example. There was an article I read that I won't be able to replicate with the same image- but we'll try anyway!
Take a look at this 'person' on the left:
[here]
You can formulate quite a few opinions based on what you're seeing without knowing anything about them.
Now go to paint and add the words:
'' I think I'm ugly'' and you'll formulate more opinions
Edit the clean image again and add these words:
'' I think I'm gorgeous'' and your new opinions about this person may contrast.
TL;DR... If you know nothing about the person and you just walk past them on the street once and once only - your opinions on their style will be different and more veered towards physical appearance.
If you know something about the person and you just walk past them on the street - your opinions on their style will be different and veered towards comparing the type of person you believe them to be.
...
and 
. Assuming that there's no problem with accessibility/financial/are wearing what they want. They tend to dress alike. Has the same hairstyle, makeup, etc. In that sense, they have the same branding/one to many. But when the media or other people see them, they are perceived to have very different styles(what I mean by many to one). Why?
