In the copy I edit I am frequently coming across constructions like his wife Gertrude.*
Let’s think this through.
If Gertrude were a daughter and the construction were his daughter Gertrude, we could infer that the man has more than one daughter and we are singling out the one named Gertrude. If the construction were his daughter, Gertrude, we could infer that the man has one daughter, whose name we are supplying parenthetically.
Now, what can we infer from his wife Gertrude? (1) He has more than one wife, and we are focusing on the one named Gertrude, or (2) Our writer has a cloudy understanding of what commas are for.
*If you think that the sentence should have read such as rather than like, you are mistaken, but we’ll take that up another time.