2/3
A look in to old callbooks on archive.org shows DL9DX mentioned early as 1952 with the Name Josef Stammen. Last entry there is from 1995 with the name Hermann J. Stammen. So it seems to me, that the callsign could somehow be inherited from father to son (that is speculation).
And kind of a sad reminder that you are not the first owner: you get a QSL card you can not verify against your logbook. Then you check the date and realize: that QSO was before your time.
#HC04S @hamchallenge