Thanks to Tollkühnheit we know for a fact that multiple people can have a full Grutrissheit at the same time.

The situation between Rozemyne and Ferdinand is unique to them, due to their mana being so similar that Erwärmen can’t tell them apart. But Gervasio has completely seperate mana, which means if he can pass “Gramp’s” test, and doesn’t fumble the receiption of the knowledge, he will get his own fully filled Grutrissheit just fine. The former one being the bigger if.