First everyone should be aware that the Bible was written in Greek, Hebrew, and Aramaic. So right at the start we can say that the KJV isn't the original Bible. It's merely the first English translation.

So two things....

1- keep in mind when the KJV was being translated that Hebrew was a dead language. Our ability to translate Hebrew much more accurate since That time allowing us to have more precise translations of certain portions of text.

2- The science of textual criticism and transmission has also progressed and we have newer, earlier sources (Like the discovery of the Dead Sea Scrolls) that we can use to determine textual variants / changes such as those made by scribes producing copies of Bibles by hand.

"Textual criticism" is the practice of examining manuscripts to locate the most accurate among all the various manuscripts we have from the 2nd century onward. A science that has come a LONG WAY since the KJV.

I recommend a book on the subject by Dr James White, who is one of the top experts on that and a couple of related subjects, in the world.

The King James Only Controversy: Can You Trust Modern Translations? (2009)

He does a very fair examination of both sides of the issue. Even if you want to continue to hold to a KJV onlyist position this book will give you a much better understanding of the subject.