Documentation describing Log time format is too optimistic stating that year can be in range 0001-9999.

First of all, looking at the code one can notice that negative timestamps are discarded, therefore lower bound is Epoch year of 1970.

Secondly, even if the system's native time_t is 64 bit it is implicitly converted to int and int is used throughout Zabbix to store timestamps. On most systems int is 32 bit (and even this is quite optimistic, C standard explicitly requires just 16 bits), therefore year range 1970-2038 is more realistic.