The VITAL standard or IEEE 1076.4 was first published in 1995, and revised in 2000.
The version of the VITAL packages depends on the VHDL standard. VITAL 1995 packages are used with the VHDL 1987 standard, while VITAL 2000 packages are used with other standards. This choice is based on the requirements of VITAL: VITAL 1995 requires the models follow the VHDL 1987 standard, while VITAL 2000 requires the models follow VHDL 1993.
The VITAL 2000 packages were slightly modified so that they conform to the VHDL 1993 standard (a few functions are made pure and a few one impure).