On Wed, Jun 29, 2016 at 1:21 PM, Random832 <random832@fastmail.com> wrote:

But if I were asking that question in real life, I'd say "Before or after the time change?",

I disagree. By asking this question, you are introducing an additional knowledge that is completely unnecessary - the moment of "time change." The actual problem is very simple: you have a spelling such as "Nov 6 01:30 AM, New York Time" which happens to be ambiguous. You want to choose between two moments in time that can be described by this phrase. It is quite natural to enumerate them in chronological order and this is exactly what the fold value does. There is no need to explain what happens between these two moments and when. Note that the difference between the two questions is not purely scholastic. In popular system interfaces, finding the moment of "time change" is difficult, so requiring it to be known for the simple task of disambiguating datetime instances in the fold is impractical.

which is understood by all to be an upcoming time change from DST to non-DST.

No way! It is hard enough to remember Spring-forward/Fall-back. Remembering which one is to and which is from DST is impossible. Pop-quiz: what does S stand in EST? (a) Standard; (b) Summer. And in DST? :-)

A more compelling argument is that it applies equally to *other* time changes such as a region adopting a different time zone offset.

Yes, this was an important motivation.