Correct; that bushing is commonly not replaced. It is almost always still good, even in a high mileage trans.
U = used, N = new, either one should come with the bushing already installed.
I have not changed one of those bushings for... well... a LONG time... working in a trans repair shop we have lots of cores and parts.
If I get a center support with a bad bushing, I just go grab a good used support off the shelf.