I am trying to gain insight about the process by which vocalists identify their voice type or fach. I am not looking for any discussion about the basic distinctions between, say, soprano and alto. Voice types, such as coloratura soprano or lyric soprano, often overlap in many ways. There are several factors including range, tessitura, and voice color, that go into voice type, and as I said, there are various overlaps between types based on these qualities. Further, the roles associated with some fachs can be performed by those in a different fach.
Still further, these types are only categories; every human voice has its own unique characteristics that may generally resemble one type or another, but may have interesting quirks. Lastly, the voice evolves over many many years, generally not settling until late 20's or even 30's (and even that might not be the end of it), further confusing issues regarding specific voice type.
My question is, with all of this ambiguity and complexity, how does a vocalist and their teacher reach conclusions about what voice type they belong to? How does that process evolve over time?
I should note that I am fairly familiar with this process from first-hand experience as a sometimes-singer, although I'm not really looking for information for my use as a singer but to better understand singers as a conductor. I am looking for specific anecdotes and/or knowledge from singers who have gone through this process of discovery.