TL;DR: I'd say we go on a case by case basis. Starting the writing of 'there is no established etiquette' may not be as much of a fix as you think. I'd recommend extreme caution when editing primarily opinion based or 'what should I do' questions into asking 'what is the correct etiquette in this situation', and to not be too easy in saying that 'there is no established etiquette' is an answer and thus a reason to leave questions open. This includes just adding an etiquette tag to questions that otherwise don't mention etiquette at all, the tag alone doesn't make a question an etiquette question.
The first (i think) cited etiquette question roughly uses the terminology "Would a woman be breaking a rule of etiquette if X" which is good, but a new user might write "can I do X" or "should I do X" for the same effect and be shoe-horned into the "What should I do?" category when really the question is about etiquette in the same way the cited wedding dress example is.
Here's the actual title of the question, which summarizes it a little better than your summary: 'Does the "never wear white to a wedding" rule of etiquette only apply to weddings attended in the United States?'. I agree that, if this were phrased something like 'Should I avoid wearing white to a wedding in the UK' and the question body still contained the reference to the US rule of etiquette, this is something an edit could easily fix. This is a clear cut case of someone basically asking Does this rule of etiquette apply in my situation. There's no real reason to put that on-hold as primarily opinion based, and indeed the answer to such a question may be a more elaborate version of what you're proposing in your own answer.
As for your Exhibit A (now deleted), I wouldn't see this as a great etiquette question. I feel the way it was phrased was still asking more about 'what should I do' than 'what is the etiquette in these situations'. It held the most potential of all three questions, but the whole question was edited a lot, excluding e.g. what their 'thoughts' are on tipping, whether or not tipping was sensible etc. as such phrasing invites 'bad answers'. (see more on this later in this answer). There also was no mention of etiquette, except for the tag you added. An attempt was made to fix this question. OP declined this, so I rolled back the edit and deleted the question at their request.
The same goes for Exhibit B and Exhibit C, they need editing and careful rephrasing to invite good answers. I see for example your answer to C, and your answer contains no references to etiquette, just one to a medical claim. They may be closed for entirely different reasons than just having an answer of 'there is no etiquette'. If you see a question that you think should be reopened, feel free to make a specific post arguing for it's reopening on meta.
Be careful with the editing part though: There's been a lot of questions asking 'what should I do'. Almost every one of them could be rephrased to 'what's the etiquette for dealing with this situation', or 'how do I communicate X'. Most of the time, this leaves a technically on-topic question that still lacks the necessary details for answering.
So just always editing a question to ask 'is this appropriate' or 'what is the etiquette for X' isn't a magical fix, and leaving them open just to allow answers to those types of questions saying 'there is no etiquette' ... Well, I'm not a fan.
This is a quote from a chat I had with HDE, from when I just started on IPS and was wondering about those questions asking 'Why do people do X':
My acid test for those is whether or not the behavior is widespread. If it is, then maybe there's a common reason. If not, it becomes a person-by-person case, and perhaps Too Broad. transcript
I'd like to apply that to etiquette and social conventions too. So, if you think there actually is enough social convention/etiquette, then perhaps you can edit a question to be about such. If you think it's not, it's likely to be opinion based or too broad/unclear and closing it will do no harm.
In response to your answer, I think the above needs clarifying a little more. Were you to ask a question like 'What colour dress can I wear to a wedding in the Netherlands', I would think it's not a secret that weddings are pretty formalized and ritualized in places, and that there is likely to be an etiquette for it.
Most people living in X country will be able to tell you whether or not A is an established etiquette or not.
That's true. But then there's still A. There's still some rule of etiquette, or some behaviour, that's being asked about. For me, this falls under the part where we can safely say 'Nope, A isn't an established etiquette over here, I know because I worked the bridal shops for years'.
The question asking about the wedding dress is already asking about a specific rule of etiquette we know exists somewhere. Questions asking about whether or not a rule of etiquette exists for a situation at all are a totally different kind of question though.
There have been a few 'etiquette' questions that have asked this, that have been left open, and where the answer was that there was no specific etiquette:
These have something in common though: They both, to an extent, carry a goal: The first one says it's important to keep a polite, friendly and professional relationship, and the second one is trying to keep good relations to the group moderator. In these cases they are still pretty black on white, in cases like Etiquette regarding borrowing of power tools the 'goal' is a lot more implicit, but the tone of the question still suggests 'keeping good relations with the neighbour' is a goal/premise.
In almost all our good etiquette questions (that aren't about 'does this rule apply under X circumstances), people are basically asking 'Is there a specific etiquette for this situation that I can follow to hopefully reach this goal'. I think that's a good intermediate solution. Answers that then say 'no, there's no etiquette' can be treated like any other answer, and still be held to answering the question as is, perhaps answering what can be done to reach the goal.
A question like 'What is the etiquette for dealing with evil neighbours' with a body of 'Here's all the evil things my neighbours do, what is the etiquette to deal with them' isn't likely to be helped by an answer saying 'I've lived with neighbours all my life, there is no etiquette for this'.
Instead, it's better to handle this like any other 'what should I do' type question: Ask about the goal the person has, what they'd like to achieve by 'dealing with their evil neighbours'. So, not all etiquette questions that have as their answer 'there is no etiquette' should be left open by default. It's perfectly fine to close an etiquette question as 'primarily opinion based' or for asking 'what should I do', if there's e.g. no real apparent reason as to why the question was asked.
The main issue I see in closing an etiquette question for this reason is that it assumes people will be answering "badly".
Well, questions need to be written in such a way that they invite good answers. Take a look at for example the Good subjective, Bad subjective blog post: Out of 6 guidelines for good subjective questions given at the end of it, 4! are related to the kinds of answers a good subjective post should invite, this includes inviting backed up answers. If people see a question that's not doing this, they're free to close or edit such a question.
Much like a don't answer this acknowledges that OP wrote a valid question, but explains why OP shouldn't do something (or in this case why there is no etiquette).
As for those 'Don't do it' answers, we've had a lot of discussions on what makes a 'good' don't do it answer since. This is the most recent post on writing such answers. Basically, a good 'don't to it' answer includes another way to reach the goals set out in the question, it for example answers a question about telling something with 'you better ask, here's why'.
I don't think we can really explain why there is no etiquette. Is it because we looked on Google and found nothing? For about as long as IPS has been existing, we've tried to get rid of answers saying 'There is no Interpersonal Skill for this':
I don't particularly like answers that say "There's no interpersonal solution here." Two points spring to mind:
- It's very, very hard to show that there's no interpersonal solution to an interpersonal problem.
- It's very, very easy to claim that there isn't and then write a non-IPS answer.
Have you considered what would be the back-up for saying 'There is no established etiquette for this'? Would a quick Google search suffice? A Google Scholar search? An exhaustive search through anthropological research materials dating back at least to the 1500's?
Allowing questions asking 'what is the etiquette for X' allows for answers saying 'As far as I'm aware there's none, but here's a way of doing X'. Out of the three answers that question got, this is the only one left standing. The other two were deleted, for saying things like 'offer a donut' or 'do X', without even referring to etiquette at all. Do we really want questions and answers inviting such answers? Now we're out of HNQ this may be manageable for a bit, but what are we going to do as the site grows and the quantities of such answers become higher and higher?
We already have quite a lot of expectations for answers on IPS. Do we really want to add more for etiquette questions, make exceptions to established rules like the above on writing answers saying 'there's no interpersonal solution here' just for etiquette questions? For me, it might make the site more confusing instead of easier to use, new users don't realize we treat etiquette and interpersonal skills differently and start applying the wrong 'standards' to both questions and answers. It will add another point to the already steep learning curve for participating on IPS.
Can we please start writing "There is no established etiquette" answers instead of closing valid questions as primarily opinion based.
I'd say we go on a case by case basis. If the 'what is the etiquette' question is no more than a thinly veiled 'what should I do' question, it should be closed. If it can be edited to be a proper normal IPS question, or a proper etiquette question, feel free to try and edit. If the question is already about whether or not a specific and proven rule of etiquette applies under specific circumstances, such a question is likely to remain open and otherwise it's editing and reopening can be discussed here on meta.