Welcome to CCF. The series 1996 $100 New York district went all the way up to the AB-Y block, so AB-X was not the end of the line. The 1996 $100 New York district star notes ended at serial number AB19200000*. I'm not sure what you mean by one-of-a-kind since serial numbers are not duplicated, all of them are. Condition is everything, please post a photo when you can.