World with default settings - no clockwork mobs

Today, I generated a new world based on default settings. However, there is no clockwork knight, bishop or rook. I even tried c_gonext("knight")/c_gonext("bishop")... but the server responded with "Could not find any objects matching 'bishop'/'knight'". 

The dedicated server version is 2006932. The worldgenovveride.lua contains:

return {
  override_enabled = true,
  preset = "SURVIVAL_TOGETHER",
  overrides = {
    --(...)
    chess = "default",
    --(...)
  },
}

This shouldn't happen because the DST update changelog of "HOTFIX 193331 - 10/14/2016" has the following fix:

Quote

• New worlds are guaranteed to contain a Maxwell Statue and at least one Clockwork Knight.

Can anyone tell me if it is possible with the aforementioned config files to have a world generated without any clockwork mob?