It should be noticed that this glyph and Sb2-1 are of another sort than the rest:

Sb2-1 and Sb2-7 the rest of the periods

I think that e.g. Aa7-72 also might belong to this special type of glyph:

Aa7-72

Significantly also Aa7-72 is located in association with what I believe to be a calender for the year.