The reply is very well thought out and very nicely formatted.
I have however a few comments about some details
In KiCad, all ground symbols are designated as “Power Output” terminals.
The power symbols are invisible power input pins! This makes them a global label. In addition to this ERC will then check if another pin on the same net is a power output. (If no power output is on the same net you get the error “pin connected but no pin to drive it”)
They also have a special power flag (note the reference “#PWR” in each of them). This creates a global label for your circuit with the name of the ground.
This is also not quite right. The # at the beginning of the reference ensures that this symbol is not added to the bom or connected with a footprint.
I am not sure if the reference must be PWR. My guess is it can be anything really.
There is however a “this is a power symbol” flag in the symbol definition. If i remember correctly then this flag is used to identify libraries that should appear in the “add power symbol” dialog.
Sadly i can not add a comment to this answer on stackexchange as i do not have enough reputation. @Seth_h could you look into these comments and fix your post over at stackexchange? (I will then happily link it from the FAQ index thread)