All Christian literature that isn`t published by the Borg is considered apostate literature simply because Christendom itself is regarded as apostate and does not agree with WT/JW teachings.
Funny thing though WT/JW accept the findings of the early apostate church as to what books should be included in the Bible and of course not wanting to align themselves with Catholics they sided with the protestant version.
Another funny thing { to me anyway } is their acceptance of the name "Jehovah" for God a name that was invented by a Spanish Catholic monk of the 13th Century simply because it was in common usage by an organization they definetely view as Apostates ?
On the one hand the claim Christendom hid the name of God Jehovah and on the other hand they claim it was the most familiar name in Christendom ?
Which is it WT/JW ?
The name Jehovah has been inscribed in stone on Churches throughout the world since the 13th Century.
The WT printed a publication for the 1963 (I think) International Convention that had photo`s of Churches all around the world that either had the Tetragrammaton or the very name Jehovah inscribed in stone on centurys old buildings.