The official word. . .
In response to the question posed by the OP, anything you see in RadioReference should be treated as unofficial information. While we're flattered that some public agencies use RadioReference as a source for programming information, and we strive to ensure that its as accurate as possible, we make no guarantees as to the accuracy of the data, and anything used for official radio programming purposes should always come from the appropriate agency.
While it's true that many alpha tags in our database are the actual "official" alpha tags, it's also possible that they're a variation of the "official" tags created to make them more user-friendly.
For example, Podunk PD's actual dispatch talkgroups might be DISPATCH 1, DISPATCH 2, DISPATCH 3 and so on. However, someone not from the area might wonder who that is. So, the alpha tags could be altered to read PPD DISP1, PPD DISP2, and PPD DISP3.
And as Voyager notes, some "official" alpha tags are so cryptic as to be unintelligible, unless one were to know these things. So, such alpha tags would be edited to be more scanner-friendly.
That being said, we encourage use of the official alpha tags wherever possible to avoid confusion for the user between what's heard on the radio and what's seen on the display, but reserve the right to edit as needed for clarity.