"Today the tropical year is defined as the period of time for the ecliptic longitude of the Sun to increase by 360 degrees. Since the Sun's ecliptic longitude is measured with respect to the equinox, the tropical year comprises a complete cycle of the seasons; because of the biological and socio-economic importance of the seasons, the tropical year is the basis of most calendars." (Wikipedia)

Time flows and therefore March 21 (the conventional date for 0h) 'does not count' and the first of the 'notches' (glyphs) for 'nights in the past' engraved on the Mamari tablet evidently corresponds to the beginning of the day of March 22:

March 22 (81)	23

Ca1-1	Ca1-2
koia	ki te hoea

March 24	25	26 (85)	27	28

Ca1-3	Ca1-4	Ca1-5	Ca1-6	Ca1-7
ki te henua	te rima te hau tea	haga i te mea ke	ki te henua - tagata honui	te ika

March 29	30	31 (90)

Ca1-8	Ca1-9	Ca1-10
te honu	te manu te henua

In contrast the Mayan haab calendar had day 'zero' visualized as a '0' (although only the outside of such an 'egg' is visible):

"The Maya Indians had several calendars, the one I have used here is their calendar over the year (haab). It was used in conjunction with the more famous tzolkin (for their sacred year), which was composed by the numbers from 1 to 13 prefixed to one of their 20 daynames, for instance as 13 Ahau - the last of the 13 numbers conjoined with the last of the 20 daynames (Ahau). This gave 13 * 20 = 260 possible dates according to the tzolkin.

In the picture below [Henrietta Midonick, The Treasury of Matemathics: 1.] is explained how a more definite date is generated by combining tzolkin with haab:

Also the ordinal number in the month according to the haab calendar was prefixed (see B cogwheel). But the counting began with 0 instead of with 1 (cfr for instance 1 Imix in the A cogwheel, the tzolkin). The last (19th) haab month (Vayeb - or as spelled in the picture: Uayeb) had only 5 days, and its highest number therefore became 4. Otherwise the highest number in a month was 19. Months were defined in the haab calendar, not in the tzolkin." (Copied from my preliminary Glyph Type Dictionary.)

Furthermore, the Mayas did not use some standardized outline of an unbroken egg shell but instead some non-standardized picture of a closed sea-shell, for instance:

At the opposite side of the year is the September equinox and according to the Gregorian calendar this occurs in September 22 (day 265, i.e. 100 days before the end of the year).

185	March 21 (80)	northern summer
185	September 22 (265)	180
southern summer	March 21 (445)	180

The northern summer is longer than the southern summer because the path of Earth around the Sun is not a circle but an ellipse, with Earth relatively far away from Sun (aphelion) in early July and relatively close (perihelion) in early January.

Line Cb7 has several rau hei glyphs, upside down figures, and possibly this is because of the September equinox:

September 17	18 (261)	19	20	21

Cb7-10	Cb7-11	Cb7-12 (548)	Cb7-13	Cb7-14
te hokohuki	te maitaki	te hau tea	te rau hei	te moko tanu

September 22	23 (266)

Cb7-15	Cb7-16
te hokohuki	e haga o rave hia

Another type of glyph in line Cb7 is moko (lizard). These glyphs are like the rau hei figures drawn as if they were pregnant. But instead of being upside down they are upright.

According to Bishop Jaussen there was a season when the lizard stones (te tau moko) were buried (tanu).

Tanu

To cover something in the ground with stones or soil; to bury a corpse; tanu kopú, to bury completely; this expression is mostly used figuratively: ka-tanu kopú te vânaga tuai era, ina ekó mana'u hakaou, forget those old stories, don't think of them again. Vanaga.

To bury, to plant, to sow seed, to inter, to implant, to conceal; tagata tanukai, farmer; tanuaga, burial; tanuaga papaku, funeral; tanuga, plantation; tanuhaga, funeral, tomb. P Pau.: tanu, to cultivate. Mgv.: tanu, to plant, to bury. Mq.: tanu, to plant, to sow. Ta.: tanu, to plant, to sow, to bury. Churchill.

... A une certaine saison, on amassait des vivres, on faissait fête. On emmaillottait un corail, pierre de defunt lézard, on l'enterrait, tanu. Cette cérémonie était un point de départ pour beaucoup d'affaires, notamment de vacances pour le chant des tablettes ou de la prière, tanu i te tau moko o tana pure, enterrer la pierre sépulcrale du lézard de sa prière.

In an agricultural society burials in the ground must have been strongly associated with sowing seeds - securing a new generation. The 'pregnant' forms rau hei and moko could have been intended to illustrate such regenerative burials.

The form of moko resembles the form of the hanau (birth) type of glyph - which reasonably ought to occur a little later:


moko	hanau

The bulging stomach is no longer there. Looking ahead at the glyphs in the beginning of line Cb8 there is indeed - as expected - a curious variant of hanau:

Cb8-7

Time will show if this is only a coincidence or not.