Interesting find. I notice on the 1901 Census for England - Alfred is listed living at 41 French Street Southampton. His place of birth is registered for Germany but in brackets he listed as a British Subject. The same household names on the 1901 Census does appear on 1911 Census living at 102 French Street Southampton minus Alfred. A chance Alfred is at sea possibly?? The name registered for the 1911 Census falls under John Walker. He's also on the 1901 Census with brother's -- George and Arthur.
His book of discharge can bee seen in the German National Marine Museum in Bremerhaven. It's a copy that was given to him after he lost his one on board the Titanic. And off course the faitful voyage can be found inside. You can see it on www.titanicverein.de under "Die deutsche Geschichte"
It seems that a photo of Alfred Theissinger has been found. It was published in a german newspaper alongside with a translation of Theissinger's interview (Washington Herald, 19th April 1912) some time after the sinking.
The german newspaper "norderlesen" and the german Titanic magazine "Der Navigator" reported on it.