It probably was fabricated, do you really think Germany would bring Mexico, ravaged by a revolution Mexico, into the war for... Not really any reason? I mean after Brest-Livitosk it was a whole lot easier for Germany, so why would they do that?
true, I never really know. It doesn't seem like they'd WANT the Americans to join, and the British do have a valid need for assistance because their allies were struggling, so it does seem valid that they may have faked it