Bookworm,
I think we may be talking at cross-purposes here. From a practical point of view, what the controller tracks is actually a wee icon with a data block painted next to it, that includes things like aircraft type, flight ID, altitude and destination (these items are variable according to controller taste and role, and which brand of radar display they are using, but the basic principle is the same the world over).
In a conventional Mode A environment, all that information is actually associated with the icon by a computer, which achieves that minor miracle by using the Mode A code to look up the answers which it has previously been told by entering from a data strip, or whatever. If several aircraft had been allocated the same Mode A code, the computer could become confused as to which was which.
In a Mode S environment, all the information that the controller looks at is also associated with the icon by a computer, and generally speaking, they look at exactly the same stuff - flight ID, type, altitude, etc. The only difference is that now, the computer has the benefit of additional data from the aircraft, including of course the 24 bit address. Thus, as I pointed out earlier, it is quite possible for two aircraft to carry the same squawk code without any risk of confusion. In theory the computer could also automatically load the flight ID, since that is now a Mode S readable parameter, but in practice my understanding is that not enough aircraft implement flight ID correctly yet to make that worthwhile. Altitude is of course a Mode S readable parameter, but other items in the data block, like destination, are not, so there is still a data strip to make up.
I think the point I was trying to make is that at no point does an air traffic controller look at a 24 bit address (although his radar system is using the address to speak to individual aircraft). So it doesn't pop up on the screen as 0C-14-7D and the controller says "ah yes, that'll be the 07:30 from Manchester". On the other hand, the radar displays I have seen DO show the squawk code, including the usual 12 bit codes from Mode S equipped aircraft.