Wikidata that they are or have been employed by what university. Data about this has been added categories at a time. Often this has been repeated for categories about the same university from different Wikipedias.
At the same time information has been added for the universities where people studied. However, there is an increasing number of professors for whom it is not known where they studied.
Professor Butenandt is a case in point; he studied at the university of Marburg and the university of Göttingen. It is known on one Wikipedia and not on others. Given that categories are linked as well, it is fairly easy to signal missed opportunities.
Thanks to this query by Magnus, we know about 23,351 professors without an alma mater. For Mr Butenandt information has been or will be added and, obviously there is much more work left to do.