:Additional Information is what it is all about, yes!
My short list of things to read;
Basic fundamentals of fighting scatterguns
The Defensive Shotgun - Louis Awerbuck
Stress Fire II - Massad F. Ayoob
Shotguns - DVD - Clint Smith
Any or all of these will do
The Mental arts of defense and protection
Principles of Personal Defense - Jeff Cooper
More Tactical Reality - Louis Awerbuck
The Tactical Edge - Charles Remsberg
Understanding our weapon
Complete guide to combat shotguns - Bruce Canfield - NOTE, I am partial to this one because yours truly is in it!
Streetsweepers - Duncan Long
These are some places to start, frankly I am not much of a DVD guy, I know many of these references are on DVD I have no idea where you would look.
Finally, we have a great resource right here in our forum, that's our moderator Dave McC, and I bow to his knowledge and understanding of the subject. Very little that he says do I question.
I spent several years using the fighting shotgun in combat and a longer time as a armorer keeping them running. If I can help I will, if I don't know I will try to send you in the right direction.
Good Luck & Be Safe