After an hour trying to find this same answer, and finally figuring it out by experimentation, I realized that the question HAD been answered several times already; its just counter-intuitive and not clearly explained.
Lets say an Assault Rifle Blaster creates a new SG and calls it "Kane's Killers" ... and let's say he's the 6,666th SG created on his server.
The system will confirm his SG with a message "Creating SG 'Kane's Killers - 6666'". (paraphrased)
Our hero promptly forgets that appended number. Not to worry! Each time he sets a new passcode, the system will remind him...
Your supergroup base access passcode is now NAPALM-6666
Your supergroup base access passcode is now BULLETS-6666
Your supergroup base access passcode is now CLUSTERBOMB-6666
Pretty sure there is not. As I said, I believe it is a sequential number ... IIRC, when I registered my first SG its assigned number was one greater that the total previously registered.