Well, I’m not a Scripture Scholar or anything, but here is my understanding on the KJV.
Since it’s first publication, there have been some 20,000 edits and corrects made to the King James version of the Bible.
The Old Testament version in the King James, is based on the Hebrew version of the OT, whereas, the Catholic Bible uses the Septuagint(Greek) version of the OT, which was the version used by the early Christian Church. The Septuagint has 7 more books than the Hebrew Version of the OT.
For Centuries after the destcution of Jerusalem, Jews claimed that the Septuagint was never used by Jews as being valid. However, the discovery of the Dead Sea Scrolls proved them wrong, in that they contained both the Septuagint and Hebrew versions of the OT.
Also, 80% of the Old Testament references and quotes made in the New Testament are in the Septuagint Version of the Old Testament. Use of the Septuagint OT when reading the New Testament, is more favorable.