After a couple of years or so of studying the Bible about stuff related to this subject (not necessarily on purpose at first), I'm under the impression now that the Bible itself indicates what's in the Bible and what isn't.

And the answer is that everything the Catholics (I'm not Catholic, btw) think is in the Bible is in the Bible (including the three additions to Daniel), except for the book of Jude, the Greek additions to the book of Esther, and the Letter of Jeremiah, which is included as the 6th chapter of Baruch in Catholic Bibles. And then there are five more things in the Bible, things that don't show up in Catholic Bibles: 2 Esdras, Psalm 151, Prayer of Manasseh, 3 Maccabees, and 4 Maccabees.