I mostly agree that the “fun” of this origin is tracking down new enemies for a unique and rare reward, so as you collect everything, some of that is lost. In keeping with that spirit, maybe you could get potions with very minor, random effects from killing elite enemies? It fits the anatomist theme, as the elites are exceptional individuals they’d want to study. Game-mechanic-wise, elites drop named items which provide a slight, unique, random boost to parties, so give the anatomists an extra little perk and incentive to hunt them?
Ultimately, yes, it would probably let some parties get extra powerful if they go beyond 300 days or something, but for the core game and most players, it would be fine.