How exactly is a pre-damage to be assessed?

My old Golf IV (Bj.99) got a shram in 2013 times on the fender, which was regulated according to the Haftplficht reports as follows: WBW : 1400,- EUR Rep Costs: 950,- EUR Remaining value: 0 EUR The expert said to me at the time that the car in unrepaired condition has no value and therefore no claims can be asserted in the event of another accident. Due to the high vehicle age I also have no reperature v The other day, however, the rear bumper has been damaged. Can I really give myself another test report?