I know I'm coming very late to the party, but I'd like to make some suggestions about the subject codification (perhaps for the "next" level -- if there will be one).

  1. The codes for the months (1 through 12) are well accepted and understood universally.
  2. The real problem is that the codes for the other divisions provide no mnemonic value to a human user while either constructing or deciphering a date "by hand".
  3. I believe that the codes for the remaining divisions (half, third, quarter and season) should suggest (as a mnemonic measure) the type of division to a human user.
  4. Omission of a "Northern/Southern" qualifier for the seasons can lead to confusion (or worse, inaccuracy).  Although a case can be made that since ~90% of the world's population lives in the Northern Hemisphere,  a reference to "Spring" probably (possibly?) indicates the season that begins at the March equinox.  But it also remains possible that "Spring" means the season that begins in September.  There is no way to accurately pin down the season without that pesky "Northern/Southern" qualifier.
  5. The terminology for the divisions in section 4.7.2 should also be revised.  The currently used nomenclature is a mixture of both common and more "academic" terms.  In addition, the terms are an inconsistent mix of nouns and adjectives.

My suggestions are detailed in the tables below my signature.

For what it is worth,
     Tony Benedetti

Suggested
(all common nouns)

Current
(mixed common & "academic"
nouns & adjectives)

month month (common noun)
half semestral ("academic" adjective)

third

quadrimester ("academic" noun)
quarter quarter (common noun)

season

season (common noun)

Division Suggested Current Notes                                                                    

Month

1-12 1-12
Half
(Semestral)
1st
2nd

21
22

40
41
Beginning the code for halves with "2" will become recognizable as the "division where a year is cut into two pieces".
Third
(Quadrimester)

1st
2nd
3rd
31
32
33
37
38
39
The same could be said of "3" and "... into three pieces".

Quarter


1st
2nd
3rd
4th
41
42
43
44
33
34
35
36
Look ... it works for "4" too!


Sixth

1st
...
6th

61
...
66

I've slipped in a 2 month division ... might be useful for bimonthly periodicals

Season - Northern
(default)
Spring
Summer
Autumn
Winter

81
82
83
84

21, 25
22, 26
23, 27
24, 28
Okay, so now we have to use an arbitrary first digit.


Season - Southern


Autumn
Winter
Spring
Summer
91
92
93
94
29
30
31
32
The Southern seasons have their own 1st digit.  In that way, we preserve the notion that a second position of  "1" means the first season of the year.  The order of the season names is reversed for the folks who live South of the Equator.  The first full season of the year is Autumn -- followed by Winter, Spring and Summer.