It was late ... I was tired ... and I've never been very good at arithmetic. For those reasons, I managed to forget to include "days' in my suggestion. Here's a corrected and properly formatted version of my previous post.

Ask me "What time is is?" and I'll tell you how to build a watch.

My apologies,
     Tony Benedetti

Thu, 25 Jan 2018 01:32:55 -0500
Here he goes again!  Please note that this is a suggestion for a subsequent ISO/EDTF -- NOT for the publication looming on the near horizon.  ... Thanks, Tony

After observing the "seasons discussions" for a while, I've come to believe that humans will not
routinely be able to prepare or interpret any values other 1 through 12 in the "MM" segment when
dealing with a date.  That is, unless they use a "cheat sheet" to decipher the meaning of "47". 

I've also noted that the current schemes -- while trying to make dates usable for humans -- are problematic for computers.  Notably, sorting dates is not possible without first checking to see if rearrangement of the data is necessary and then making any adjustments.

It seems that we are rolling a rock up a hill and are trying to serve two very different goals -- human
usability vs. predictably precise computer-to-computer data interchange.

Thus, I'm certain that there must be at least two representations of a given date.  The first is an
internal encoding for the computers and can provide the necessary precision and predictability.
The other representations are for humans to consume and are appropriate for a given application
and audience.  There are already several programs available on the Internet that -- with various
degrees of success -- translate EDTF dates into natural language phrases.

So let's develop a scheme that will eventually allow the computers to encode and decode a date
string and allow agents (computer and human) to present an appropriate human readable value.

Here's a (radical?) solution that might work for a "Level 3".

Many (most?) of the potential {calendars} represent an edge case.  But I think the only corner case in the scheme is the poor guy with a pencil and a "cheat sheet".

Render unto Caesar the computer the things that are Caesar's the computer's; and to God the humans the things that are the human's.

Tony Benedetti