Is "if you're not familiar with X, it is..." or "if you're not aware, X is..." correct English?

The only source of potential confusion that I see here is that "If you didn't know..." can be used in two distinct senses;

• as a hypothetical, where this "if" portion of the statement is an assertion and the rest of the statement is meant only in the context where that assertion is assumed to be true

and

• as a way to state the intention of the statement

These examples seem to be cases of the second. Here the "If" part of the sentence operates similarly to "Happily" as it is sometimes used at the beginning of an utterance. My intuition is that it is not a part of the parse structure of the sentence, but instead a piece of metalanguage regarding the nature and intent of the speech-act itself.

Other common examples which I take to be of the same nature (at least pragmatically speaking -- I expect that the syntax would vary substantially at the deepest level):

Obviously, if you see something printed frequently it is likely to be grammatical in some sense.

or something even stranger, like

To be certain, the syntactic structure here is not clear or obvious.

(Note that there are not many infinitives that could comfortably take the place of "to be certain" here, which indicates to me that something strange is happening at a level that is not naively syntactic)

I think the parse here has a structure like:

Utterance : {
              meta/prefix : { some-stuff-indicating-context-or-feeling }

              content : { A-normally-structured-sentence }
            }

In conclusion, it is important to bear in mind the flexibility of language and its users.

It seems to me the instruction is correct enough; it's a contraction of an if/then statement of sequential parts of one thought: if X then Y; followed by the understood, offered elaboration."If you are unfamiliar with X (then I will provide for you/direct you to an explanation/description and here it is): ..." It's a rhetorical device by which the writer/speaker offers casual intimacy and unoppressive authority.

These appear to be standard introductory clauses to me. I've second-guessed myself a few times in trying to find other things wrong with the examples, but nothing's coming to me. Perhaps, if you're not satisfied with this or other responses, you might consider trying to better explain what you think is wrong.

EDIT: I don't mean to make this seem as clear as it may appear to native speakers. I believe this to be a related construction to beginning a sentence with an adverb in an otherwise apparently ungrammatical manner. For more on that, see Grammar Girl's article on "Hopefully." It is an idiomatic construction that is common enough to be recognized by folks like the Chicago Manual of Style, which takes its cue in this case from Webster's Dictionary and the Oxford English Distionary. The reason you're seeing it more often is that the AP upgraded the construction in 2012.

Stop worrying about "correct". You've already found evidence that very strict and well educated editorial staff considers it acceptable.

Grammar is not fixed, regardless of what people who write books or pose as experts on the internet tell you. The practical questions are: how many people will find the meaning unclear, how many people will understand the meaning but feel that it sounds funny, and how many people will have no idea why anyone would think it sounds funny.

In this case, the answers are, in order: no native English speaker, maybe a couple of people who like to act smarter than everyone else, and over 99% of native English speakers.

There are already a lot of lengthy answers, but I think all it comes down to is deletion...

If you haven't heard of X [then let me tell you that] X is the greatest thing since sliced bread.

Where everything preceding "X is the greatest..." is simply the preamble.

In practice, of course, the speaker (it's usually a spoken or informal written form) isn't going to refrain from telling you what he wants to say, even if you happen to know it already. Nor is the "truth" of his substantive statement in any way contingent on your prior knowledge. (Obviously the relevance is affected - but as I said, that's not going to deter the speaker from pressing on).