Don't forget some scanners can display "False" talkgroups.
The alpha tags (last I looked in the DB) are pretty correct for what is/was actually displayed on the radio's. Should be no more than 8 characters.
With the purchasing of the newer XTL and XTS radios, it may be expanded, but the talkgroups and purposes will be the same. The XTL2500/5000 can have 14 character zone AND channel names and the XTS's can up a total of 14 characters on the display (one line only). Typical config is a 3 character zone name (usual Z1 ) ((space after the "1" so there is a space inbetween the zone and channel name) with the rest being the channel.