We encounter small differences between the numbers we expect for special glyphs and their real numbers. This can be due to a wrong choice of where to start counting. Or it may be due to misunderstandings - about what the glyphs mean or what the numbers mean.

One example is Gb1-21:

Gb1-16 Gb1-17 Gb1-18 Gb1-19 Gb1-20 (250)
Gb1-21 Gb1-22 Gb1-23 Gb1-24 Gb1-25

It is not number 250 counted from Gb8-30, it is number 251 (or 64 + 251 = 315 counted from winter solstice). Gb1-21 is - it seems - not the last glyph of 250 (or 314) but the first glyph in a new part of the calendar.

Hau tea at Ca9-23 could be a parallel to Gb1-21:

Ca9-17 Ca9-18 Ca9-19 Ca9-20 Ca9-21 Ca9-22 (250)
Ca9-23 Ca9-24 Ca9-25 Ca9-26 Ca9-27

Venus determines 8 years by 5 of her cycles. It is probably no coincidence that 25(0) and 64 are combined in the texts to reach 314. Because 5 * 5 = 25 and 8 * 8 = 64.

Interpreted from this perscpective, Gb1-21 and Ca9-23 could be parallel and indicating where next Venus cycle is beginning.