When you leave out something like the Ascension, yes, that's a huge difference. You must understand that until the 4th century, there was no one unified Bible in print form - there were scattered books, and while it was generally believed that the various churches under their bishops knew what was truth and what was forgery, that was not universally the case. Christendom has never been in possession of a complete, original text of all of Scripture - in fact, no "original" texts exist. As such, when we've compiled Scripture, we've never relied upon solely one source document, as we've been forced to rely upon multiple. This gives rise to the variation in translations (NIV, KJV, NASB, etc). The translation of books of the Bible referenced in your cite - the Codex Sinaiticus - has often been used as part of a translation but in context with other manuscripts and fragments (ie, the Codex Vaticanus, the Biblia Hebraica, the Septuagint). So in short, none of them contain the complete truth - they've required cross-referencing and research. But if you doubt the Ascension because books are missing from the Codex Sinaiticus, you should accept the Ascension because those books are present in the Codex Alexandrinus.