Reverted edits
Even a dead language can have words for new concepts. It's dead but it's not absolutely forgotten and forbidden. Linguists still care about that language and try to implement new words into it. There's a word for computer in Latin. Do you think Romans had computers? There's a word for computer even in Old Church Slavonic (ищислитєл҄ь). I don't see any reason why срьбьскохръва́тьскъ ѩꙁꙑ́къ shouldn't be an option. It's even on Slavonic version of Wikipedia. Don't take me wrong but I think your "didn't even exist" reason is kind of irrelevant.
Well, if I got it right, you mean the "Reconstructed languages" part. It's not the same thing in my opinion. It's not like PIE or some absolutely forgotten language where you can just guess. It's not guessing. It's just how it would be. Even more with Serbo-Croatian where it's just combining of words.