1. The Lutheran Scholastics do not view Scripture as a sort of flat line of revelation. They distinguish within the NT between Homologoumena and Antilogoumena. Articles of the faith, established by the clear passages of the Homologoumena (sedes doctrina) cannot be established by the Antilogoumena. In the same way, the OT is divided into the OT proper and then the Apocrypha. Apocrypha is at a lower level than the Antilogoumena in that it is an important witness to the truth, but it is not inspired. The Antilogoumena is viewed as being less certain apostolic kerygma, not definitively non-canonical. Nevertheless, the Apocrypha is viewed as being a witness to the truth.
2. So, the whole thing works on a beautiful methodological hierarchy of sorts: The clear passes that teach specific doctrines (sedes doctrina) interpret the less clear passes. Christ the center interprets them all- like spokes on a wheel. The whole makes up the analogia fide. So, the analogia fide make the Homologoumena clear. From this perspective the Antilogoumena is authoritative, but is interpreted by the Homologoumena. The New Testament then interprets the Old Testament (which is equally clarified by the clear passages within it by it's own sedes doctrina). The Apocrypha then also can be cited as an important, secondary witness to the truth.
3. This methodology is based on a Christocentric assumption about the authority of the Bible (the hierarchy of authority within the Bible has to do with dominical authorization) and about the content of the Bible (the Bible is meant to witness to Christ). It also assumes that Bible is self-interpreting (Rom. 12:6 is frequently asserted as forming the foundation of the analogia fide method).
4. The interesting thing in practice though is that Antilogoumena is quoted as if it is equally authoritative as Homologoumena. The most glaring example of this is the Formula of Concord. According to Robert Preus, Chemnitz was even more extreme than Luther on this subject and literally thought the Antilogoumena should be thrown out of the Bible. But when one reads the FC, Hebrews, Revelation, etc. is quoted without any qualification. One finds a similar phenomenon in Gerhard regarding the Apocrypha and I've also found it in many other Lutheran Scholastic authors. They quote the Apocrypha even in sections that deal with the prophecies of Christ (Wisdom being the best proof text in this regard). It's as if they thought that the Holy Spirit came down for one moment and inspired the author, just to withdraw moments later. This aspect is highly puzzling.