Can't help with specific years, but I know the 642ND was available in the 90s, as that's when I got mine. Unless something has changed recently, both the 642-1 and the 642-2 are currently being made.
642-1
Introduced in 1996 with the J Magnum Frame.
August 1997, all barrel markings were moved to the left side
of the barrel leaving the right side blank.
642-2
Introduced the internal key lock system in 2002.
2002 change from 4 address lines to two lines.