We do understand that not all "Car to Car" and "TAC" channels are that, right?
I know of many agencies that refer to their chit-chat, or business channel or talkgroup as "TAC" as an identifier, but there is no "Tactical" action being undertaken. It sounds cool, it's easy, people know it means not-the-main channel, what have you, but I have yet to see a Fire Department performing any "Tactical" actions...yet all of them in my county have VHF simplex channels they call "TAC" on the air...albeit they should be listed as something else, like FIREGROUND.
"Car to Car" is simply a way to do the same thing in a LE agency where they need to relay information without bothering the dispatcher. Where I am from this is a left over from the Low Band half-duplex days where you would switch the car radio to the Base TX frequency as a means to talk to another car directly.
Designations are often misused in the world. Not every copier is a Xerox. My local Sheriff's departments people will go to "Talkaround" on thier radios....except they think it is another channel, seemingly not realizing other cars can still hear them, and they may be talking over the dispatch if they are close to another car who is not in the conversation....ironically they hardly ever go to their "TAC" channel, repeater or talkaround, which is where they should have the conversation anyway, and it should be labeled "Car to Car" since no tactical action is taking place. Of course they have a NPSPAC UHF Simplex programmed, and they don't know how/when to use it either..... If a channel is truly tactical in nature, it should probably be encrypted anyway.