I'm looking for some help understanding Ground Stops and Ground Delay
Programs...

In order to reduce arrival rates airports have the following 'tools' to
use...

1. ask a flight in the air to 'Slow Down'
2. ask a flight in the air to 'Hold' over the airport
3. issue a 'Ground Stop'
4. issue a 'Ground Delay Program'
5. other

My understanding is that Ground Stops and Ground Delay Programs only
affect flights that have *not* left the departure runway yet. So, once
in the air a flight cannot be affected by the Ground Stop or Ground
Delay Program tools, but can be affected by the Slow Down or Hold
tools.

Is this correct? If I was, for example, creating a report of all
flights affected by a particular Ground Stop or Ground Delay Program,
can I simply ignore the flights that departed *before* the Ground Stop
or Ground Delay Program was issued?

Thanks.