This is an issue that many debaters struggle with, especially when both sides are using research that seems to support their side but from different sources. For example with the Spring 2016 topic, that China should introduce a Carbon Tax, a lot of debaters argued "Country X's carbon tax doesn't apply to this debate because it's not China and so it's not relevant!" This argument annoys me, and I think that in its most basic form, it isn’t valid. It's only valid when made in the presence of specific, detailed analysis.
There's an idea called the "principle of relevant difference" which is that you should only treat two things differently if there is an important difference between them. This is actually a very obvious and common-sense idea. If I asked you to choose between a plate of salad and a plate of dog poop, you would choose the salad. If I asked you to choose between a plate of dog poop and a plate of cat poop, you wouldn't care which one. Dog poop is different from cat poop, but that difference isn't important in this context: they're both disgusting.
So you can only dismiss an example from a different context if there's a good reason why it doesn't apply: a relevant difference. The key assumption of a carbon tax are that if prices go up, demand will go down. This is a basic economic law and I cannot think of a single country where this law is false.
In fact, it is often better to make predictions based on analogous cases than based on the case you are planning for. InThinking Fast and Slow, Daniel Kahneman calls these "The outside view" and "The inside view". Governments, for example, consistently underestimate the time and money required to for big projects like railway systems. Kahneman shows that looking at the time and money required to do a similar project in a different country gives better estimates than building up your own estimate based on what you know about your project. When asking a question with a quantifiable answer, taking the outside view–-studying other cases–-is actually more accurate if there is a collection of reference cases available to consider.
If you want to say that Sweden or Denmark or Ireland's carbon taxes are different, you will have to work harder than that. You will have to do more than just say "but it's a different country!". I admit this argument will work on unprepared debaters–I have watched it defeat them many times–but you need a way to beat strong debaters too, and strong debaters will not fold so easily.
Denmark is more windy than most countries, both in Europe and around the world. Besides this, winds are stronger off of the coast, and Denmark has a high ratio of coastline to interior land. Because of this, Denmark has a lot of land where windmills will return a lot of energy and therefore money compared to the price of building them. In other words, Denmark has special access to cheap wind power which other countries do not. Since Denmark's alternative energy miracle would not have happened without wind power, this shows that Denmark's success doesn't apply to any other country. This sort of argument would be sufficient to disqualify Denmark.
By the way, this is a very portable lesson. All sorts of debate topics are full of example cases, and those example cases are always different from what you're proposing. Otherwise, the resolution would propose that we do something we are doing right now! In every topic, remember the principle of relevant difference, and use it to separate good examples from bad ones.
Of course, you can argue the reverse. You can argue that examples should be assumed to be irrelevant until they are proven to be relevant by showing relevant similarities. This strategy was used successfully by the winning team in the final round at Dalian. But this approach is a double-edged sword: it can hurt you as much as your opponents. They can say that the same rule applies to the examples in your case.
This is a specific instance of a general lesson: if your opponents impose a tough standard on you, impose it right back! If your opponents complain that your evidence is too old, make sure all of their evidence is newer. If they demand that your impacts be countable and specific, demand the same of them! Or attack the standard and argue that neither team should have to follow it. But never agree to have the debate under a set of rules that disadvantages you.