Board Thread:General Discussion/@comment-26006155-20190820122909/@comment-26006155-20190829230752

The thing is, we have no idea how fast the monster population grows. Each different type seems to be a completely different race.

And Flowey's soul vaccum blast that drew in all the souls (except Frisk and the ghosts) in the Underground also made the snails in Blooky's snail farm vanish. Those snails were technically monsters.

(Which means that the Dreemur family have been eating MONSTERS for dinner, just like the spiders have been eating spiders. I have no idea what this means, but it's creepy.)

So doing 'math' about the monster population, as well as unknown quantities like Chara's hometown, really is just another layer of glorified guesswork.