There tends to be at least two viewpoints when it comes to dupes like this. There's the specific question side, and there's the game mechanic side. This is what's coming into play here. We have the new question being specific, and we have the game mechanic question designed to handle the entire scrap mechanic.
The specific question type is generally what we get here from new users, as they have their specific problem with a game, and they're just looking for an answer. This is the narrower viewpoint, and is scoped precisely for the user. This is their exact scenario, and they're looking for a answer on how the game plays out in a specific use-case.
In the best case scenario, this hasn't been asked at all in either form, we can let it stand, and everyone's happy. The wonky bits happen when we get specific questions, and we already have a general question about that mechanic.
The game mechanic side looks at the entire mechanic behind the question. How does X work? What can I do to influence this to my advantage? Are there related mechanics I can game to influence and gain an advantage? This has no actual scenario attached to it, because it's looking for everything that influences this mechanic. In a perfect world, we'll catch every variable attached to the mechanic, and note how it's influenced by it.
Therein lies the clash between the two viewpoints. We have a question about a specific scenario, and how it influences scrap. We also have a general question about scrap, and how to maximize your gain of such. The specific scenario being discussed is encompassed inside this question, we've just had the bad luck of this variable not being addressed in the general question. If it had been answered, and wasn't buried, this wouldn't even be a problem. We'd dupe it and leave it.
When we get such a clash, I think what we should be doing is figuring out how much effort it would take to update our existing answers to take that scenario into account. If it would take two or three paragraphs or more to fully answer that scenario, I say don't dupe it. That amount of information can be extremely useful, and will help anyone else who needs it. If adding a sentence or two can account for that entire scenario, though, that's a modicum of effort to encompass the extra scenario. For that, I say dupe the specific question to the general mechanic one, and update the answer to include it.
Now, the question is, how much effort would it take to update our general question with this specific information?