There are many ways these P25 systems can be configured. I suppose "by default" if you didn't customize any of the configuration, then yes, all talkgroups and subscribers would be allowed to operate on any site/band. That works fine for a small system with few sites that everyone needs to be able to operate on, however for a large regional or statewide system, it can make for very inefficient use of precious channel resources. As the vast majority of VHF sites of the STARNet system are comprised of only 3 frequencies (1 control + 2 traffic = 4 voice slots), it wouldn't take much to quickly saturate a site with traffic that it doesn't need to be carrying. And thus, the admins almost surely restricted talkgroups to sites where they are actually needed for coverage.
In the end, it really doesn't matter what talkgroups DCNR is using for testing, it's all the same coverage regardless.