I tend to agree with what was said above about it probably only referring to revelation but as it is put we don't really know for sure so better to just leave it all alone. It is interesting to think what books could have been added to the bible but did not make their way into it. I have heard about books that were intended for the bible but were left out for some various reason or another. I try to think of it this way, if god had intended something to be added to the bible it would be, if he wants it to be left alone then it will be. Whatever he wills comes to pass.