[quote=@The book of bad juju]
I live in a town of 120.000 people and i could not for the life of me tell you what everyone does in it. There are neighbourhoods i've never been too, streets i've never walked down, and i've lived here all my life. Danzig, as wikipedia could tell you, is a city of 366.730 citizens.
[/quote]

True. But you probably WOULD be aware of each other if, say, you all had a mutual friend (Kyubey) and worked the same job, competing over the same prey. At least to an extent. Even with a steady population of witches, you would probably bump into one another enough that you would be familiar after a month or so.