Great question, Helmut! I've struggled with that issue myself. With no sources, or only second-hand references to someone's compiled tree, it is impossible to know which name is accurate. When it is just a spelling issue, I add the other spelling in the Other Last Name(s) field and add a note at the top of the Biography section to indicate that a source is needed for the last name. When there are two different names, such as in your example, I avoid the merge because I don't know what the correct LNAB is, and I don't want to create a possible incorrect redirect. One time I rejected a merge request and stated that the profile needed a source to prove the correct LNAB first. I received a stern message from the profile manager who stated that I should "just merge" and let her do the sourcing later.
I hope someone can provide us with a better solution.