[king_jester]

A lot to respond to, so I'll just make it brief. How to handle someone who has transition is well covered on the internet. Also very common on the internet is bad faith arguments that fret over whether they should or should not accept certain aspects of someone's transition. Simply put, just accept that transition and use basic phrases if you must refer to something about that person's past presentation. However, don't always bring it up or bring it up without need as you are basically performing a subtle misgendering of the person by always throwing that past presentation in the face of their current presentation, which is something that happens a lot for trans folks.

[kbenson]

I'm not trying to reject anyone's transition, I'm trying to figure out when, where and why it was decided that the past description in this case gets rewritten for the current context instead of continuing to to exist in an accurate form.

For example, we don't refer to a block of marble as a statue until it has become one. When referring to its past, we don't generally refer to it as a statue until it has become one. I was a boy before I was a man, when referring to that period of my life, expect anyone to refer to me as a boy (or child), and not my current state.

To be absolutely clear, I have no problem referring to someone as they desire in the present or future, but I've yet to see a good reason (beyond "it's disrespectful!", with little or no explanation) why a change in name or gender requires a rewriting of history. I would be happy to have an argument put forth I could get behind, it would hopefully make this less confusing in the future, and cause less friction if I misstep.

[sesqu]

While a single entity can have multiple identifiers, one is usually canonical in a communication environment. For example, we say "Istanbul was founded in the 7th century BC" when speaking of the present-day city, But we say "Byzantium was founded" when we wish to limit the discussion to the pre-Constantine era. If we wish to span multiple eras, Istanbul is the only choice, as that is the canonical identifier.

As such, I believe you should refer to Manning as Chelsea if she is the subject, but may refer to her as Bradley if the leak is the subject. It would be helpful to qualify her name as "Chelsea Manning, who was at the time known as Bradley", "Bradley Manning, who later changed her name to Chelsea", or some similar construction for audiences who are not well aware of her, to help them connect historical knowledge to your topic.

[kbenson]

This is perfectly sensible, and exactly what I was looking for. It chooses the most relevant and least confusing identifier for the context it was used in. The question then becomes, "Is this acceptable to the transgender community?" and "Is this in common use?"