I've got three versions of the companion. I think thats all there is?
I have the first one in hardback, then the paperback version of that one with 'revised and updated' splashed on the cover and a third soft back, taller book with the Librarian in some kind of occult book setting (funny symbols and dribbly candles galore) on the cover!
I personally think they made a mistake in editing out old material for the third 'revised' version as I would dearly love one compendium, or at least release the companions as versions covering book 1 to whatever etc.
But then, I am a bit of a geek.
I might follow and adapt Tonys tongue in cheek advice and start glueing all my copies together!