Kai.Grossjohann@CS.Uni-Dortmund.DE (Kai Großjohann) writes:
> I don't know whether it helps to add the in-reply-to header to
> gnus-extra-headers. 

No.  On the other hand, it doesn't seem to me that it would be too
hard to add an (or ...) clause around accessing the overview-supplied
references with an in-reply-to extraction from the current article.