Here's the thing:
Games Workshop has set up a channel for delivering their 'official', binding (as binding as any tabletop gaming rule can actually be) rulings, that being their errata and
FAQs.
ANY other method they choose to disseminate information from, regardless of who is providing that information, is not official, because of the mere fact that they absolutely do have those official channels.
Yes, information given by the games designers about a rule is absolutely helpful towards giving gamers a good idea of how that
might be ruled once it gets in an official
FAQ/errata, but until it actually shows up in an official
FAQ/errata, then whatever the games designer says via Facebook, email, twitch, etc., is still just an opinion that may or may not be later changed.
Long ago, in the mists of time when I used to edit/write the unofficial
INAT FAQ for
40k, I used to have back channel connections to
GW rules writers. And I can tell you from firsthand experience that more than once I talked to a rules writer about their intent behind a murky rule and how they were going to handle said rule in their official
FAQ. The rules writer told me (again, on more than one occasion) how they were 'planning' to
FAQ something, and we ended up ruling that same way in the
INAT FAQ. Imagine my surprise when, months later, the official
GW FAQ comes out and they ruled the exact opposite way! The first time it happened I was flabbergasted. The second time it happened, I was not surprised.
The reality is, even rules writers can get something wrong or change their minds later after getting more feedback on the issue. That's why companies have official
FAQs and errata. Its so there is an easy place for players to go and find the official, condoned rulings put out by the company.
Answers/rulings provided via other sources can be posted in
YMDC. And in fact, it can be incredibly useful to get that information out to people because it is *likely* that
GW will rule that same way when they address the issue in an official
FAQ/errata. But when you post a ruling from an ancillary source, it needs to be done with the understanding that it is *not* official, and anyone posting it like it *is* an official ruling is ignoring the fact that
GW does have an official channel for their rulings (and facebook, twitch, etc, is not part of that channel).
As such, I've added another sub-point to the tennents of
YMDC:
2a. Rulings via GW's social media accounts, twitch streams, etc., even though often provided by the actual games designers, are still not considered official rulings by GW until they are actually published in a errata/FAQs. As such, while it is fine to bring up rulings provided this way in YMDC, it must always be couched with the understanding that these are not official, binding rulings until they actually make their way into a errata/FAQ.
But I'll let you in on a little secret:
In
YMDC (and on the internet in general), you will never, ever, ever, ever convince the person you're arguing against that they are wrong. The only thing you can ever hope for is to make a salient point and know that the dozens of people
READING the thread (but not posting) will see what you write, think it makes sense, and will agree with you...all without you ever hearing from them.
Posting unofficial rulings from
GW's ancillary channels in
YMDC can be incredibly useful towards this point, because most people recognize the value in such rulings knowing that they give a *likely* sign of how
GW will rule on an issue (even though it isn't 100% until
GW actually puts in a
FAQ/errata).
Just post these types of things in
YMDC, admit when you're doing so that you know they aren't official, drop the mic and walk away. 99% of the people reading will see the info you posted and choose to play that way because they know it will be the likely outcome anyway.