Assuming next that instead there are 30 days (= glyphs) in every month of summer, we must arrive at Gb5-2 after 9 months, not at Gb5-11:

Gb4-33	Gb5-1	Gb5-2	Gb5-3	Gb5-4	Gb5-5	Gb5-6
268	269	270	271	272	273	274
Gb5-7	Gb5-8	Gb5-9	Gb5-10	Gb5-11	Gb5-12
275	276	277	278	279	280

9 * 30 = 270 measures 9 months of the 360 days in a regular year, while 279 would measure 9 months of a year with 372 days (which obviously is wrong).

The reversal illustrated with Gb4-33 and Gb5-1 marks an important calendar point, and we have earlier noted how it is located at the beginning of the 4th quarter of the text:

2nd half year		116			10		106
	Gb1-7		Gb4-33	Gb5-1		Gb5-12
	236		353	354		365
	3rd quarter of text			4th quarter of text

With Gb5-12 (haga te pau) as the 365th and last glyph (day) of the year it seems to indicate how the year is ending after 9 months, viz. after 9 months of summer. 471 * 75 % = 353.25.