A name is different than a label.
Name: a word by which a person or thing is known
Label: an identifying or descriptive marker that is attached to an object
So a label might have your name on it, but often it has something else on it, such as a warning, or description, or classification.
A rule of thumb is that names are unique(ish) and labels are not.
In the example question, it looks like the word you want is "name".
Consider this website: the question's name is the question headline itself: "Is the usage of 'labeled' preferred to the usage of 'named'?". The question's labels are its tags: "usage".
Edit:
I just noticed your edit to this question. The third and fourth sentences carry the same meaning as "named". You are "called" by your name, usually. I'd use "named" or go with the fourth option, which just names the method. There are lots of synonyms for "name" but, importantly, "label" isn't really one of them.
Edit 2:
Google's built-in dictionary defines label as
a classifying phrase or name applied to a person or thing, especially one that is inaccurate or restrictive.
This strengthens the notion that while labels are related to names, names are not a subset of labels (though labels might be said to be a subset of names).
Firstly, a master's degree is not proper and therefore does not require capitalization, but personally I've seen several highly professional institutions spell it both ways.
Seeing as how all three of those sentences are grammatically sound, it's more a question of etiquette or regional custom. Like Peter Shor was saying, it's not wrong to say that you took your master's degree in somewhere but you may have to use caution repeating prepositions.
e.g. I took my master's degree in astrophysics in the University of Somewhere
Using in twice is potentially awkward in situations where you may need to elaborate on your area of study.
To answer your question, all of those examples are grammatically strong and should get the message across appropriately anywhere you go.
On an editorial note, however, there are some ways to bypass this dilemma by opting for more colorful words:
I (received, earned, attained) a master's degree after (studying in/at, attending, graduating from) the University of Somewhere.
Play it right and you'll sound like a Nobel Laureate, but all of your sentences will work well; none of them is really noticeably better, even on paper.
Best Answer
They are both suitable, but the difference between them is that hereinafter (sometimes written as two words, herein after) usually pertains just to writing within a document, While henceforth is more general, and just means from now on. For what it's worth, I've only ever seen hereinafter in legal documents (my rent contract, most recently).
So, for example, you could say:
but you could not say:
Within the context of a document, either might be used, but hereinafter specifically limits itself to the document or corpus in which it appears. Therefore, it is often the preferable choice for coining a replacement term or phrase:
That does not mean that you cannot write henceforth in a document, however. For example, you could write:
Hereinafter would not be appropriate, since it places too much of a limit on the scope of the author's claim.