The Plus call Grand Swing Thru introduces the idea of a "Grand" call. The difference between Swing Thru and Grand Swing Thru is that in the Grand case the people in the very center trade with each other.
More generally, "Grand" changes a call that is normally done within a four-person formation into one where all eight people work together. Instead of the dancers staying strictly within their group of four, the people in the very center interact with each other. How, exactly, they interact depends on the call, but it is usually obvious from the nature of the call.
Here are the "Grand" calls used in A-1, listed along with the corresponding four-person calls:
|Four-Person Version||Grand Version|
|Swing Thru||Grand Swing Thru|
|1/4 Thru||Grand 1/4 Thru|
|3/4 Thru||Grand 3/4 Thru|
|Scoot Back||Triple Scoot|
|Follow Your Neighbor||Grand Follow Your Neighbor|
The Grand version of Scoot Back might have been called "Grand Scoot Back", but the name Triple Scoot is used for historical reasons.