I'm embarrassed to admit that I did not know this until just now - some eastern Christians have a 3 & 4 Maccabees in their Old Testaments! Just goes to show that the idea of the canon is an organic thing. Thankfully, all Christians have the same New Testament (as far as I know). But as important as the OT is as background for the NT, the OT seems a lot more "fluid" as to its boundaries, especially in the early Church. At the end of the day, this is further support for the insight I wrote about in Reading Scripture Like the Early Church, that the early Christians read the OT and the NT differently. Both are the inspired word of God for them, but one might go so far as to say that they are inspired in a different way, or in any case, they are meant to be interpreted differently.

Looking for a middle way here, one extreme would be a functional Marcionism or gnosticism, that is, reject or ignore the OT as irrelevant. The other extreme, practiced by a lot of conservatives I think, is to hold up the OT as being on the same level as the NT, and erroneously read it as though it sometimes takes precedence over the NT in interpretation (I go into that in the book). But ironically, a lot of progressives make the OT more important than the NT when they mine it for prophetic passages that they can interpret according to their political agenda. So I guess the middle way is exactly what the early Christians did: treat the OT as inspired, but in the sense that it informs the NT, yet the NT has a certain priority for the Church, which is to say that you interpret the OT in light of the NT, not so much the other way around.