Could the inverted maro in C have the same characteristic, be the first glyph of a new major part of the text? Cb11-18 is like Gb1-7 located on side b, but not close to the beginning:

			76
Cb11-17	Cb11-18 (662)	Cb11-19		Cb14-19 (740)

There is a horizontal break between the left tagata part and the right inverted maro part, as if to indicate that the glyph is straddling a division.

So far we have identified maro glyphs at summer solstice and at winter solstice, and also an inverted maro at 8 lunar months:

summer solstice	winter solstice	8 lunar months
Ga5-15	*Ca14-23	Gb1-7

If we are lucky we will find Cb11-18 at 16 lunar months, it would complete the group.

An investigation is necessary to find out.