First of all the mythological aspects. Even if it should be so that the Easter Islanders who wrote on the rongorongo boards were filled to the brim with mythology, and even if this mythology was congruent with Greek, Egyptian, Indian, Tiahuanacian etc mythology, why necessarily believe that should have been reflected in their texts?

Astronomy, mathematics etc comes first, mythology later. That means, e.g. that the turtle flipper in the legend about Hotua Matu'a which my imagination saw reflected in 1aP and 1aQ (Pb5-1 and Qb5-130) not necessarily was in the minds of the writers.

On the contrary: It might have been these two glyphs (and others on rongorongo boards now lost) which influenced this legendary tale. Certainly the tale is talking about the difference 365 ¼ - 360 and very probably the 1a text is also talking about that, but the ideas behind the tale could very well be the rongorongo texts. Astronomical and mathematical knowledge presumably was transmitted with the aid of rongorongo. That knowledge then influenced the contents of myths and legends.

The tale was influenced by the tail seen in the glyphs. In the glyphs the tail is a reasonable outcome from efforts to illustrate ideas of an end or ending - cfr the sun-boat in stone. It is not necessary to presume that the tale about a turtle and 6 men with one of them injured by a flipper to have influenced the sequence of glyphs.

Though of course (and indeed most probably) it might have been 'hen and egg', a mutual influence and development. Hens, eggs and myths are old, old. And a 'tale' might like a 'tail' mean the last part of something.