I do not base my faith in God based on the historical errors of the book - only on the spiritual works.
The Hebrews themselves did not create the bible as a history - in fact history as a was created by the classical Greeks centuries later. The bible was created as a spiritual guide rather than a history lesson.
Passages that exist in newer manuscripts but not older ones may certainly have been introduced later (and I'm especially inclined to believe that they were when the grammer, vocabulary, style, or other details point to the hand of a different author) but some also could have come from an oral tradition or other even older manuscripts that no longer exist to compare against. There is a lot of oral mythology built into the interpretation of many Bible stories that are not clearly supported by the text. They could be later additions or could very well be based on authentic oral history or earlier variants. For example, I'm not entirely convinced that a "Q" existed or that Mark, per se, was a major source for the other Gospels. As the non-canon Gospel of Thomas shows, the sayings and acts of Jesus travelled around verbally in many forms, just as the Quran did. We don't know what all of the original sourses were and there may have been even more material that once existed that has now been lost. The similarities and differences could simply reflect was different communities remembered.