It doesn't matter.
Any 12" toilet will work fine on the longer rough's, they just stick out in the room more.
Will a new 12" rough in toilet (Toto Drake CST743S) work replacing my old toilets which were put in further away from the wall? One of my toilets is some 16 inches from the wall to the bolts, with few inches of "wasted" space from the wall to the tank. Why does the 10, 12, or 14 inch standard matter, if I don't need to save space?
A good idea is to use a piece of wood or something to fill that void between tank and wall, anything that keeps those who use a toilet like a lazyboy recliner when using them. It happens more than you think, and it puts undo stress on the brass bolt heads on the toilet. Unexpected leaks can follow as well from the movement. Something a simple as a old magazine like a reader's digest have been found upon replacing a toilet to "shim" the tank against the wall. Some ideas for thought.
Read what the end of this sentence means.
I stayed in a motel recently where the toilet was almost an island. It sat 18" to 24" from the wall. I would fear someone might accidently lean back too hard, so I'm with Rugged on the idea of blocking. For appearance sake, you might even want to consider building the entire wall out or at least from the floor to above the top of the tank.
I've never blocked a tank to the wall.
Most tanks don't touch walls. I prefer that they don't.
I've never had a call from a homeowner with the problem mentioned above.
I guess that's just one more reason for some to go with a one-piece.