• The royals have not searched the Academy (and specifically the Academy Library) for the Grutrissheit nor would they have thought to since supposedly only lay and mednobles ever go there personally.
• IIRC, Mestionora's shrine in the library is depicted holding the Grutrissheit
• The Archnoble librarians who might have been privied to royal secrets were purged.
• "Gramps" would mean something even older than the Schumils in the library and the only thing we really know of thus far that would be older than them is the Grutrissheit
• When Rosemyne touches the Grutrissheit on the statue it sucks an enormous amount of mana from her
• After the magic is sucked out nothing of note happens. The only other time a huge amount of magic being consumed without anything immediate happening is with mana offerings
• The Schumils assume Rosemyne - as their owner - is royalty and therefore supplying the country with magic would be part of her duty

I also suspect that Ehrenfest's Foundation is located in the Temple bookroom behind the shelf with Mestionora on it. If Mestionora is responsible for giving the Grutrissheit to the first King then it would make sense that aspects of government would depict her. This would also explain Ehrenfest adopting prayers and other Temple customs into their culture when other duchys do no such thing. Further, Ehrenfest's Bible seems to be an extremely accurate version given that it has the extra magic circle and hidden messages, implying that Ehrenfest was originally founded with very strong ties to religion/the Temple.