On recommending, reusing and attributing existing answers in almost-duplicate questions

Question

It seems that many questions I considered duplicates aren't viewed as such by a decisive amount of users, therefore I'll need to adjust my response to these questions¹ and I would like to ask for some guidelines on how to answer them.

Let's consider for example possible questions that could appear under the Harry Potter tag:

A) How many Horcruxes had Voldemort made?

B) Describe the Horcruxes made by wizards/witches in Europe in the XX century.

a fair amount of questions like these could be created, all of which probably could be regarded as different, standalone ones, while they still could be answered by the same, often already existing answer. It is not a problem, as it is often repeated here on meta:

answers don't make questions into duplicates.

Ideally, an answer to questions A) and B) would contain data such as the name of the Horcrux creator along with the description and names of all the known Horcruxes appearing in chronological order, supported by canon references. Now, we have an answer here by Slytherincess, which perfectly answers both questions with maybe some minor adjustments.

Another example would be the recent question Why does Turanga Leela and her family put their surname first? which probably would be adequately answered by gnovice's answer especially after their latest edit, with simply emphasizing the 'we don't know about the existence of any canon origins' part as a header.

So what would be the recommended action, when a user² posts a question if a good answer on the subject already exists on SFF?

Should we direct OP to the answers of existing, similar questions and try to answer the new question only if OP states that the existing ones are unsatisfactory or perhaps we should attempt to answer the question right away, without an attempt to enlighten OP about our current resources which may provide an answer to their inquiry?

If we decide that an answer is required to OP's near-dupe question should we utilize our stack (which is full of quality answers many of which kept up to date), that is, base our answer on existing answer(s) that fit³ by perhaps asking the author of the original answer to repost their answer⁴ to the new question with slight modifications or maybe we should quote or reword the old answer with attribution / link ⁵ , adding only parts which are lacking in the old answer? Would that be recommended or perhaps we should 'reinvent the wheel' and ignore altogether the original answer and write a similar or maybe even identical answer based on independent research?

What would be the best approach?

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<sup>1. Until now I've simply VTC'd them as dupes
2. especially if it's a new user, see Rand's answer
3. an analogy would be maybe not duplicating code
4. If they're still an active user, naturally
5. links would be also useful for maintenance, (i.e. adding newly released info on the subject to all the relevant near-dupe questions for consistency and clarity)</sup>

Answer 1

TL;DR: if the questions are different, the answers can often be tailored differently to each one (and if the questions aren't truly different, they're dupes and don't both need to be answered).

Main meta already has a pretty thorough canonical faq post about this from a CM: Is it acceptable to add a duplicate answer to several questions? In this case, I think the third section is most important, since you're assuming the questions aren't (likely to be closed as) duplicates, and spamming/astroturfing is a whole different ballpark which may require mod intervention.

Copying and pasting the same answer to multiple questions can cause different reactions depending on what answer you're pasting. The acceptableness of this behavior ranges from "highly frowned upon" to "completely unacceptable". (Note that it never reaches the "acceptable" end of that spectrum.) If you catch yourself or someone else doing this, please evaluate the answer and see if there is a more correct thing to do.

Are the questions duplicates of each other?

Duplicate answers most often indicate that the questions are asking the same thing. If the questions could be considered duplicates of each other, only post the answer to the best one, which you think would make the better candidate for the other one to point to. Flag or vote to close the other one so that it can be directed to the better question which has your answer. [...]

Are they promotional in any way?

Duplicate answers across questions that promote external links or resources are considered astro-turfing and will likely result in the immediate deletion of all the answers involved. Most often, these answers get posted to questions which are only remotely related to the link or product they're trying to promote, and they often consist of little more than a vague explanation of what the link contains or what the tool does. Depending on the degree of astro-turfing and status of the account, a wide range of punishments could get issued, from a simple warning to account destruction.

Could the answers be more specific to each question?

If you've gotten past the other two questions, your answer may just be too vague. Answers that solve over-generalized problems are not as useful to questions — they should be tailored to address the specific needs that each question has outlined. If linking something, explain the relevant parts to the OP, or explain how the code or tool you've linked is relevant and useful to them. Don't just throw out answers thinking "this is relevant" — explain how it is relevant. It's not always so obvious.

Are the questions asking about the wrong thing?

Sometimes, superficially different questions may indeed be symptoms of the same underlying problem. For example, the questions may describe different errors observed in different situations, all of which have the same root cause. Or the questions may all be suffering from the X/Y problem, with the same underlying problem but different poorly attempted solutions. Such questions are not obvious duplicates, and marking them as such without explaining why they're really about the same root issue may only leave the asker puzzled, yet they all have essentially the same fundamental answer.

If you've written a clear, detailed and comprehensive answer to one such question, explaining what the underlying problem is and how to solve it, it may be tempting to copy-paste the same answer with minimal changes to other questions that it applies to. Indeed, if you edit your answer enough to make it specifically fit each question, this may not be completely unacceptable.

That said, it's usually better to find (or ask!) a question about the actual underlying problem, and post your comprehensive answer there. You can then either vote to close the other questions as duplicates (with an explanatory comment, if it's not obvious why they share the same cause and solution) or just answer each of them with a short description of how that particular symptom arises from the shared root cause, with a link to the question about the cause for more information.

For an SFF-specific example of what's discussed in the last section, see Should we rewrite the 'lightsaber colour' question? In this case, many questions about specific lightsabre colours were closed as duplicates of one which was asking about a different specific colour but which had a detailed canonical answer. This caused some confusion due to the questions being different, but eventually we solved the problem by editing the original question to ask about the general case, which made it a much clearer dupe target for all the rest.