I leafed through the book yesterday and only found another signature from his son in it, I was sure there were a few more in it, maybe I "overleafed" them
During my research I found out that the World Fantasy Con 2013 will be held in Brighton and both Mathesons are listed as participants, sounds very intriguing!
World Fantasy Convention 2013 -- Welcome
Edit: I could take the book and ask Richard to cross out "Steve" and write "Rafael" instead - I wonder how he would react to that...