FayeDunaway:
Not all translators add "else" to Col 1:17. But some do.
NAB, (1970) “He is before all else that is. In him everything continues in being.”
CEV: “God's Son was before all else, and by him everything is held together.”
NLT: “He existed before everything else began, and he holds all creation together.”
Notice these translators add "else" to the Greek idea of "all" or "everything," the same way that the NWT add "other" to "all" in 1:16, but with a different agenda.
So, to use your argument that the NWT is adding to Scripture, Trinitarians are guilty of the very same thing.
The fact is that translators have to adapt their English idioms to translations from both Hebrew and the Greek. There is no way a translator can avoid altogether adding or removing some words from the original when doing translation work. It is fair to say, that both Trinitarian and non-trinitarians are "sincere" in their translation work. But they both err in the interpretation of the text. Bible readers end up choosing whatever fits their religious agenda best.