Valid group IDs are 1 thru 16776415. So you really need software like DSD+ to determine the proper value. That being said many MANY users around me use 1, 10, 100 etc... But some are seemingly totally random.
Yep, I've seen group codes ranging from simple programming (1,2,3...) to using zip codes, phone numbers , and completely random numbers.
Interestingly, every Cap+ ive encountered has simple programming.
I thought I remember reading Cap+ TG values are limited?
Another note and option, if you don't want to run DSD is the CS750 radio. Apparently it can be set to "monitor" mode where it will unmute for any group code received. You'll still need the CC, frequency, and slot of course but it is a step in the right direction and as close to a "scanner" as you can get.
DSD Plus downloaded from dsdplus.com (not the other freeware malware infested sites) is definitely the way to go IMO.