What is the correct usage of "throwing shade"?

Like other words and phrases, slang doesn't operate under copyright protections that require future users to use the words or words in precisely the manner that its originators did. If such rules did apply, a judge might very well rule that the 1980s meaning of "throw shade" and "thrown a shade" that the OP cites violated the commonly understood sense of "throw a shade" from the early 1900s. From Francis March, A Thesaurus Dictionary of the English Language (1902):

Throw a shade. To darken

That being said, a Google Books search finds several discussions of "throw shade" from the mid-1990s that refer to what the OP identifies as the original slang sense of the term. Connie Eberle, Slang and Sociability: In-group Language among College Students (1996) includes this brief comment on "throw shade":

It is often through films that the American public is exposed to the distinctive vocabulary of African Americans and homosexuals, and it is likely that borrowing from these groups takes place more through films or television than by personal association. For instance, the expression throw shade 'humiliate exceedingly' moved beyond gay and African American usage and into the slang of college students in 1991 after the appearance of the film Paris Is Burning.

Eberle seems a bit quick to conflate gay slang and African American slang into one "distinctive vocabulary," and her implicit notion that college students as a class have little overlap with either homosexuals or African Americans is rather astonishing. Nevertheless, her understanding of the source and sense of "throw shade" in college slang during the 1990s may well be accurate.

Two other Google Books matches focus on the gay African American subculture from which "throw shade" in its modern sense seems to have arisen. Both articles are well worth reading at fuller length if you're interested in the subject. From Tricia Rose, "An Interview with Willi Ninja," in Microphone Fiends: Youth Music an Youth Culture (1994):

R: Before we go, define "throw shade" for me.

N: [Laughter] Shade is basically a nonverbal response to verbal or nonverbal abuse. Shade is about using certain mannerisms in battle. If you said something nasty to me, I would just turn to you, and give you a look like: "Bitch please, you're not even worth my time, go on." All with a facial expression and body posture, that's throwing shade. If I want to be a little extra nasty I might throw in a little cough, but not so loud, just a little bit like: "You're making me choke."

R: It's definitely a challenge.

N: Definitely. You're looking for trouble when you're throwing shade. It's like watching Joan Collins go against Linda Evans on Dynasty. Or Jasmine Guy on A Different World, going against Diahann Carroll who plays her mother ...

Or when Bush ran against Clinton, they were throwing shade. Who got the bigger shade? Bush did because Clinton won. Bush threw some good verbal daggers, but Clinton just paid him dust. Clinton threw the biggest shade when he looked at him with a little smirk on his face as if to say: "That did not even work." When they had that town debate and Clinton walked toward and addressed the audience with his back to Bush, he was saying that he did not need to address Bush, that Bush was beneath him and the audience. He was saying: "You're out of the circle." That's throwing shade. Everybody does it.

And from E. Patrick Johnson, "SNAP! Culture: a Different Way of Reading" in Text and Performance Quarterly 15(2) (1995), reprinted in Performance: Media and Technology (2003):

The nonverbal counterpart to reading is called "throwing shade." To throw shade is to ignore a person altogether, even if the person is in immediate proximity. If a shade thrower wishes to acknowledge the presence of the third party, he or she might roll his or her eyes and neck while poking out his or her lips. People throw shade if they do not like a particular person or if that person has dissed them in the past. The effect of throwing shade in this manner is also a type of dissing, because it is considered disrespectful not to acknowledge someone's presence. In the playful mode, however, a person may throw shade at a person with whom he or she is a best friend.

As an example of how uncontrollable slang is, however, we have this discussion in Eve Oishi, "Reading Realness: Paris Is Burning, Wildness, and Queer and Transgender Documentary Practice", in A Companion to Contemporary Documentary Film (2015), most of which consists of a description of children's slang that was in use by 1993:

Jackie Goldsby offers a valuable refinement of this discussion by pointing to the power relations inherent in the act of "reading" as opposed to "throwing shade" or "shading":

In the ball world the children clarify the workings of power in signifyin(g) exchanges because they split the notion into two forms: "reading" and "shading." Where the former is an insult that occurs between dissimilarly advantaged speakers, the latter happens when two similarly positioned speakers square off to spar verbally. ... To “throw shade,” on the other hand, one addresses an equal on the sly. (Goldsby, 1993: 114)

Evidently, by 1993, children in schoolyards somewhere in the United States had already substantially altered the notion of shading to mean "verbal sparring between equals," not "silent disrespecting of a disliked person," as in the previous two examples. In fact, it isn't altogether clear that the schoolyard sense of the two terms wasn't the original sense of those terms. But that's the crucial feature of slang: It emerges by word of mouth—without a dictionary definition to tie it down, so it's hardly surprising that different understandings of a particular term may exist in different places at the same time. And over time, of course, the picture can get even blurrier.