We must maintain a count of the population of Narsis. With so many already fled to Mournhold, the number we have to work with has dwindled significantly.
If we abduct too many of the villagers, the Llodos plague won't have enough victims to take hold of, nullifying the entire purpose of this experiment. Luckily, the nobles who believe everything will be just fine refuse to leave their houses and remain ripe to contract the plague.
As it stands, there should be enough people remaining to spread the plague efficiently once the pieces fall into place. Even so, we must continue to maintain our list. One miscount could affect the potency and reduce how far we can spread the disease.