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As does rfc1591
“The IANA is not in the business of deciding what is and what is not a country.”
Like, what’s even your point?
Since the de facto territories of the two states are common knowledge, you can unambiguously refer to them just by mentioning their rough position on the map. Similarly, East/West Germany were not officially called East/West Germany, and it was not the official name of either country, but people still understood what the words meant.
Not since the early 90s.
Well actually it's a bit more complex since there are multiple parties and they disagree, and there's some nuance (e.g. "one China" but without actually defining what that means, exactly). But "Taiwan claims to be the legitimate government of the whole of China" is woefully outdated and incorrect.
Not according to the international community and international law.
The majority of the UN recognised countries, 106 do not recognise it. Whilst only 94 do.
The same way that Afghan democratic government melted away, when the US troops withdrew, so will "Kosovo" go.
A majority -- 102 of 193 -- UN members do recognize it. You may be counting some (though with your number, I think not all) of the false claims of withdrawal of recognition by other states which have been issued by the governments or state-affiliated media of Serbia and/or Russia, but later refuted by the governments in question, as being true.
Kosovo will not "go" away just because you like Milosevic decide to murder more Albanians - This is completely disregarding the fact that Serbia is an island of nationalism and revisionism clinging to the past, surrounded by democracies living in the present day.
Serbia will never again have the capacity to execute on these misguided beliefs.