Now we have to secure ourselves by putting on safety belts! We are approaching a place with heavy traffic. Remember that Hb1-3 is at the beginning of side b and that the writer thought that so important as to skip 23 glyphs (or 34 if referred to Q). I believe his goal was to start side b with the second half-year (now defined as the time from summer solstice to winter solstice). Logic then tells us that side a should start at the beginning of the first half-year = at winter solstice. And indeed so it looks (which I hope to be able to explain):