Sorry, it seems that I am so concentrated on the text in question that I have forgotten you don't have it in front of you.
In a scientific paper, a method is being used as the basis for improvements and additions, producing a work that is worthy of its own paper. The German paper uses "... (nach Scientists Name, Paper Name, 2000)" to say that the basis for their method is that paper, by that scientist, in that year, but that their improvements and additions are a new method.
In all the English papers I have referred to previously, if a method is used as the starting point for this research, then that is cited as "...(after Scientists Name, Paper Name, 2000)"
But I can't get any search results to show my client that this is how it should be written.