By assuming which epoch it is and it will be clearly a separate data type from the old unix epoch. Currently the assumption is the epoch which started in 1970.

By assuming which epoch it is and it will be clearly a separate data type from the old unix epoch. Currently the assumption is the epoch which started in 1970. 50 years is long enough period of time to keep a standard and 18 years is long enough to switch to a new standard. With the updated standard it is simply epoch 2 now that is ignorant about any epochs before or after.