'Precedent' is a more or less meaningless word in international relations. Don't make the mistake of thinking that international relations are governed by any kind of set rules or that international law is like law in any meaningful sense.
Countries - some countries - may subscribe to international law, but that essentially amounts to mutual voluntary agreements. Nations agree in certain acceptable behaviours on the basis that the stability and predictability it brings outweighs the occasional limitations it requires on acting in their own interests. But this is only enforceable in the sense that the political or economic (or military) consequences would be worse than compliance.
The point is that regardless of 'international law' , countries are free to act in their best interests, weighing what they can get away with in terms or their own public opinion and relationships with other countries.
In that light, the idea of 'precedent' here is nothing like the legal term. It has no legal force, because there isn't really any such thing as law, certainly not in an enforceable sense. Instead international precedent basically boils down to "this is the kind of way we've acted in the recent past, so it's a useful guide to how awe might act in the near future". In the question's link to the Wikipedia article, you can see the arguments in this light. It is really just nations arguing that that do/don't like this kind of thing, not any kind of legal argument.
Precedent is a useful guide to how nations are likely to act in the near future, because as a rule the interests and values of a nation only change slowly over time. How one acted 20 years ago is unlikely to be radically different to how it would act now. Plus there is the additional factor that many people directly remember what was done 20 years ago, and there are now likely to be negative consequences for hypocrisy and double standards.
Conversely, most nations are rather different to how they were 100 years ago, in terms of national interest, common values and concerns (the things that drive the choices nations make), and the state of the world changes a lot on that time scale. How a nation acted 100 years ago doesn't tell you a whole lot about what it will do now.
So the reason the CSA precedent had no bearing on the Kosovo situation is partly because if was a long time ago in a different context, but mostly that none of the countries driving events had an interest in bringing up the comparison: that wasn't what they wanted to achieve. And 50-100 years from now, Kosovo will still have precisely no bearing on what happens in similar situations. It will once again be driven by the interests of the nations with the greatest ability to force events to their liking, and any use of precedent will at most be used to offer justification for what they were going to do anyway, or ignored if it is inconvenient.