I have following proofs now: (have them as pics which I took during the visit) the hard facts

1) german passport, with ID number, picture
2) Meldunsgbestätigung Einwohnermeldeamt. (certification of registartion of city Hamburg)
3) formation of a company documents from notary public and adress. This information will show up in a couple of days also in the Handelsregister(Company Registry) in Hamburg. The clients will order directly from this company the boards.