The various books we call "the Bible" had not been assembled into a unified collection at the time they were written. Each work stood on its own. So in the time each of these texts was put into writing, Deut.12:32 applies to Deuteronomy, Prov 30:5,6 applies to Proverbs and Rev 22:18-19 applies to Revelations, etc.
Various parallel texts and styles exist in each book describing the the events somewhat differently, especially in the Pentateuch. There are Yawistic and Priestly versions of the stories. There are different surviving ancient texts, differing in wording and completeness. Do we blame scribes who lived thousands of years ago for "adding or taking away"? What about those who may have incorrectly passed down the oral traditions of ancient teachings through the centuries before they were written down, are they guilty of "adding or taking away"?
What of the later Bible translators, who differ on the correct way to render ancient tongues and idoms in latter day languages? When they disagree, who is right, and who "added or took away": Jerome? Wyckliffe? Luther?
The point is, we don't know, will never know, every detail and meaning the scriptures conveyed to their original audience. Obsessing with literal word-by-word accuracy is a fool's errand, not only because of uncertainty about the actual words, but also the cultural context of the times. We are not bronze age Hebrews, and we are not middle-eastern Christians of the first century. Even if we know the ancient languages, we aren't going to grok every nuance, cultural reference, and play on words they contain--they are many, and they convey an important part of the writing's message.
The worst way to "take away" from scripture is to isolate a verse here, a verse there, separating them from the context that helps us to understand (imperfectly) what message they were trying to convey. The worst way to "add to" is patching together isolated verses between different books, produced at different times and circumstances, for different uses, into a Frankenstein monster [see date of this post!] bearing but superficial resemblance to their meaning when studied in the original context.
So if you wish to avoid "add tos" and "take aways", read it in context--each book complete from beginning to end, and using different translations. The consistent message is inspired scripture; the variations are mere human fallibility.
