The last Hamilton 992B pocket watches were produced in 1971 to possibly 1972. Over the years, we have compiled a list of the known watches and their serial numbers. All genuine last-run watches start with the serial number prefix of 4C. These are not to be confused with the military 4992B watches which also start with the 4C serial number prefix.
More information on these watches can be found here: The last Hamilton 992B pocket watches.