If I am correct, no coach has ever won the super bowl with two different teams. But considering Gruden's age and the fact that he also went to the super bowl with the Raiders, I think he has a little more potential than most coaching transplants.
This is one of those completely meaningless statistics, IMHO. How many head coaches win a ring in the first place? It takes a lot more than just coaching skill. Then you have to go somewhere else (and how many head coaches with a ring do that?) and repeat?
I don't mean to put words in your mouth, but I've heard people argue often enough that they'd rather have a good coach who HASN'T won a SB than a good coach who HAS, because coaches never repeat. And, IMHO, that's just an insane argument to make.
Would you really rather have Ken Whisenhunt or Lovie Smith than, say, Bill Belichick? Really?
FYI, in the past 20 years, exactly 5 head coaches won a SB and went on to coach a different team (Dick Vermeil, Mike Shannahan, Mike Holmgren, George Seifert, and Jimmy Johnson)*. Holmgren actually managed to get to the SB again with his second team.
Of the past 10 Super Bowls, every single coach is either still with his team or has retired (without going to a new team... yet).
My point with all this is that the numbers are so ridiculously small that the statistics are WORTHLESS.
* Ditka won a ring more than 20 years ago and went on to coach a different team within the past 20 years, so count him as well if you want.