Here's the deal.
Real EDACS radios are programmed in decimal. The binary world revolves around hexadecimal (16) in the trunked radio world. There is a pattern of blocks with EDACS as in 0-15 for Agency, Fleet & Sub-fleet.
For some reason when the BC245XLT was designed by uniden they went with the idea that sub-fleets were in blocks of 8 (0-7) which was the case in early PST 16 EDACS systems at the time as opposed to 16 (0-F) which was the case in the final G.E. version that Denver and practically all existing EDACS based systems use now.
One of the claims in the late 90's was that the 245 and 895 scanners could not display A-F properly so they went with blocks of 8 subfleets for the display. This limitation, if this really was the case back in 1999, is carried on with the current line of scanners for continuity.
If you really take a close look at how Denver has each Police district setup on their system each district has a block of 16 TG's. The Same goes for Aurora PD.
So no there are no hidden, reserved secret squirrel TG's. Just a carryover of early scanner limitations from the first EDACS capable scanners.