Wow, had my mind blown yesterday by a friend of mine, a local tech, who has been working on Superblack ('92 5.3) and Superblue ('94 4.0). He is a former locksmith, repo. driver, etc. I was going to leave my Tibbe keys to both cars. He said, “no need, I have a master Tibbe key that will fit them”. 
I was like “wth???” At this revelation, I remained there, demanding that he prove that claim to me. He quickly produced what looked like a Tibbe valet key (i.e. green-headed) and proceeded to unlock the door and start the ignition for first Superblue and then Superblack with it. I was stunned. 
My tech claimed he obtained the key a long time ago from a Jaguar dealership (I think he said he gave them $150.00 for it), being assured it will fit just about any Jaguar Tibbe key lock. I looked at it, and it didn’t seem noticeably different than the usual Tibbe key, although it had “DO NOT DUPLICATE” printed on it. Given the rather unique way a Tibbe key operates, I would think it not technically possible for there to be such a key that fits all such locks. Wow … I never knew such a beast existed … glad he is not a car thief! 