So the general consensus of some of the highest rated users here is that the official Wizards of the Coast FAQ is to be ignored when answering questions: What is wrong with the D&D 3.5 FAQ?.
This is hard for me to wrap my head around so I'm asking: at what point is an official source not enough?
The answer you linked contains this explanation of the problem with the FAQ:
The D&D 3.5 FAQ inherited the reputation of its predecessor, the “Sage Advice” column in Dragon magazine. [...] The common problem with the Q&A articles, both “Sage Advice” and the FAQ, is that they were written by second parties with no better judgment than a good DM or StackExchange contributor. Yes, Williams and his successors were employees of the game publisher, and hypothetically had inside knowledge, but in practice they mostly worked from the rules and first principles like the rest of us do. Overall, their rulings were decent, but they also published quite a few screamers. As a result, online forums and Usenet groups like rec.games.frp.dnd regarded the Q&A folks as no more reliable than a smart player, and rejected arguments that used “Sage Advice” or the FAQ as authorities on the game.
Your question is when is an official rules source not enough. But the D&D 3.5e FAQ is not a rules source. It's a source trying to clarify things, just as we are. It also lacks credibility with the community because it's just interpreting rules like anyone else so it has no specific first-hand authority, and it has made terrible judgment calls over time, so it is no better than the effort of anyone else. (Notably, they have no authority or basis on which to declare their word law.)
An official source is not enough when that official source has no credibility. The D&D 3.5e FAQ isn't a "rules source" to begin with, though.
In general, this question is "too broad..." because there's a lot of games and communities of gamers outside the D&D domain and you're asking about the problem of normative textual sourcing in general. But here's the deal somewhat specifically to this situation with some more general philosophy mixed in.
It comes down to the community of play around that game (as I point out in my answer to that question). For a variety of reasons a substantial chunk of the D&D 3.5e rules folks out there have decided "no we don't accept the FAQ." So they don't.
That doesn't mean you can't accept the FAQ, or that others don't. Feel free and use it in your game and here in questions and answers.
However, on a site like this one with votes driven by the community, those super against the FAQ can and do downvote answers that justify themselves based on the FAQ because they don't personally find it useful (even though the OP might). I don't agree with that, but one of the tenets of SE is "people can vote however they want for any reason they want - we can provide guidance on how to use your votes usefully but in the end users click the button they want to click."
In the end this is a religious problem. As gaming is distributed, there's no "authoritative source" per se - the company may have a stance, groups of gamers may have a stance, none of it really matters. The only circumstance in which it matters is in Organized Play events where the controlling group says what rules are normative in that situation. You can "not like" the FAQ but if Living Greyhawk uses it, then you are using the FAQ for that context. There is no meaningful answer to what textual authority is normative outside the rules of the specific gaming group for any game.
This isn't a discussion forum so I'll give the bottom line answer from the RPG Stack Exchange official policy perspective - there is no definition of "what's official." A source is never unacceptable, it just may pull downvotes from certain users. The D&D 3.5e FAQ is not "officially off limits" and you are welcome to use it, with the understanding that there's a group of people who don't accept it as normative. The 3.5e FAQ specifically seems to be one of the "hot-button" topics that cause conflict and mutual downvoting but that's not the case for pretty much any other game, their FAQs, their rules, etc., so the more general case isn't as much of a bother.
I do wish voters would be more... discerning in their downvotes. Not liking some of the rulings in the FAQ, or not considering it "letter of the law" normative because the books say "only other books can supersede me" is fine, but discarding the whole thing as "certainly there is no helpful guidance of any sort or peeks into RAI it could provide, I will just downvote any answer wherever I see the word FAQ" is not the level of intellectual engagement we'd like to see here on the site.
But I think that's a problem that will fix itself over time, as 3.5e recedes and newer D&D versions are deliberately taking a less legalistic approach to the game, so that arguments of this sort are harder to have.
The D&D FAQ is generally given short shrift because of the factors given in the question you link, but there is no real way to know that a particular source is considered "unacceptable" on a particular site without knowing that site's community very well. I asked that question because I had recently cited the D&D FAQ in an answer, and gotten some flak from doing so. I now know why people don't like that document, and have since stopped using it in answers, but without asking about that specific document, I would never have known.
That said, the situation with the D&D FAQ is pretty much unique to D&D, and D&D 3.5 in specific. For D&D 5th, tweets from Mike Mearls are considered a rules source, and the GURPS forums take posts from Sean Punch (a senior GURPS writer) as gospel. You're generally pretty safe in quoting any statements made by employees of an RPG company, or citing documents that company when answering questions here. If you want to be extra safe, make sure you cite actual rules text as well as supporting information from non-rulebook sources.
