Hello anendlesswaltz,
Yes, as posted above, the full list of books of the bible which Catholics use was first promulgated in 383 and made the official standard for all Western Churches in 405. At this time, the Eastern Churches only used the 66 books which Protestant churches use today.
Why do we use one set over the other if they both were being used at the same time?
It comes down to why the Bible was compiled in the first place. The Bible was specifically compiled of the books which were to be used during the Mass. There were other books which the early Church Fathers believed held extremely important teachings, like the Shepherd of Hermas or St. Clement’s Letter to the Corinthians, but these were not allowed to be read during the Mass, thus they were left out.
This comes down to the question: Why the disparity between the East and the West’s canon of Old Testament book? When the Eastern Church say that they used 66 books for the Old Testament, they did not deny the authenticity and authority of the other 7 books, they simply acknowledged that their tradition did not use them in their Mass. This was officially stated in the Quinisex in 605 by the Eastern Churches when they stated that the full official canon of the Western Church (called the canon of the Third Council of Carthage in the documents) was divinely inspired and fully acceptable to use in liturgy. The canon was again officially recognized by the Eastern Church at the Council of Florence (1431-1449).
The reason why Martin Luther removed the seven books was primarily to support his own theology, as those removed books contained theological points which directly contradicted some of his theories. His desire to remove these books came about before he found justification for their removal. His primary justification was that these 66 books were what the Jews considered scriptures after Christ’s death.
He pointed to the Jewish Council of Jamnia (c. 90 AD) as proof that the other books were not inspired. The problem with this is that the Council of Jamnia had no authority to begin with. It was just a handful of rabbis which met and tried to issue decrees in the name of the Temple of Jerusalem, despite that the Temple had already been destroyed and that the Council Rabbis did not follow the proper procedure for convening the Sanhedrin to rule on matters of the Jewish faith. Also, if you took the Council at face value, you would also have to throw out the entirety of the New Testament as it directly condemned all Christian writings.
God Bless,
Ben