[Reason077]

Right, "9 pool" means build a spawning pool when you have 9 workers. So "12 courtyard" means build an expansion when you have 12 workers.

[thaumasiotes]

I think strictly "9 pool" means you build the pool when you have 9 supply. However, before you build a spawning pool, the only thing you can build that consumes supply is workers.