Operating systems of the 1970s handling dates beyond the year 2000

[Fred Cisin]

On Mon, 19 Jan 2015, Johnny Billquist wrote:
> I don't know what is special about 1972. I always assumed they used that
> base because that's the year RSTS-11 first showed up.

That anniversary is as good a reason as any other.
1972 is one full cycle (28 years) before 2000.
1973's calendar matches (days of the week) with 2001,
1974 matches with 2002, 1975 matches with 2003, etc.