When we made that decision, as I recall back in August 2007, there was a lot of concern that we not do something that would harm the security of the passport. After studying it very hard, we came to the conclusion that, in the end, dropping the guarantor policy that we had and simply substituting the one we have now wouldn't make that much difference.
I think that was the conclusion we came to, but I can always ask the experts who were there at the time.