IAMFREE, there were no mistakes in the originals. However translators have made a few! Some were intentional. For instance, the Masoretic text, from which ALL our Old Testament translations today are made, was intentionally altered about 100 AD. One of the alterations involved taking the 'hundred' cipher out of a number of the ages in the genealogies of Genesis 5 and 11. It is when we go back to the Alexandrian LXX, dated several hundred years before Christ, that we can see the original ages.
We can see a number of other things, too. For instance, the earliest texts we have indicate that Cain may have repented! I was stunned to find that out. It is not a 'for sure' indication, but given what he actually said to God ("My crime is too great for me to be forgiven"), the question remains.
You know the argument about childbearing and what God said to Eve?
Here is what the earliest texts record as being said:
"And to the woman he said, I will greatly multiply thy pains and thy groanings; in pain thou shalt bring forth children, and thy submission shall be to thy husband, and he shall rule over thee."
It is not that her pain in childbirth should be increased, or multiplied, which is the source of so much argument today regarding whether or not Eve had children before. Of course she didn't! The original text is very clear about that.
So as important as it is to know your Bible, it is FAR more important to know Jesus Himself. And then use His Word, the Bible, as our guide in all things it touches.
No, we do not have to know the earliest versions, but we must be very careful regarding our claim that any of the translations is without error. That simply is not true. However, God, being God, all the doctrinal points are quite clear and remain unadulterated through time. For those of us who enjoy digging more, we get more understanding of other points, but the doctrines NEVER change.
And that is, I think, the most important thing. The guide remains sure.