A silver steel blade is actually a carbon steel blade. I think in the past there has been discussion if the term silver steel is just an advertising ploy or if it really means there is a tiny percentage of silver in the metal. I have seen people say yes there is and no there isn't. So since no one has assayed the metal we really don't know.
My take on this is that the Shefield Silver Steel is an alloy used that has a brighter finish to it than Swedish Steel but honestly I have several TIs and I don't think they shave any better than a host of vintage razors I have from all the well known brands. I think they do retain the edge longer but that is a function of the lead hardening process they use not the alloy.
I think its like alot of the really old blades that had wierd names like carbo magnetic, radium etc.. in those days before people had to justify advertising claims they could make all kinds of wild claims about products.