What is the last day of an ISO date range like 1970--1979?

Question

I'm not sure if the first day of 1970--1979 is 1970-01-01 and the last day is 1979-12-31.

A quick search on Google didn't throw up the answer. Most examples would give a range such as 1970-01-01--1979-12-31 which although unambiguous, is clunkier than 1970--1979 and due to the extra detail, more prone to errors.

Answer 1

In "A summary of the international standard date and time notation," Markus Kuhn 1 writes:

ISO 8601 does not specify, whether its notations specify a point in time or a time period. This means for example that ISO 8601 does not define whether 09:00 refers to the exact end of the ninth hour of the day or the period from 09:00 to 09:01 or anything else. The users of the standard must somehow agree on the exact interpretation of the time notation if this should be of any concern.

So to answer my own question, the last day of 1970--1979 is 1979-12-31 if I say that is the interpretation that I intend. Which it is!

I find ISO's lack of specification ... disturbing.