Need help understanding something with the chapters.

I am on book 1 of the PON series, the darkness that comes before.

I am on chapter 9 but i dont understand what is up with the years? the prologue was year 2147 followed by 4109, ok cool got it, some time passed..chapter 1 was 4110 MIDWINTER, chapter 2 - 4110, LATE WINTER, chapter 3 4110 EARLY SPRING?

How does that make sense? Are they not chronological?

Ch 4 - 7 starts 4110 mid spring, 4110 late spring.... Ch 7 4110 early autumn

Ch 8 4111 Autumn and Late Autumn

Chapter 9 YEAR 4110 Early Winter?

Is this just supposed to be showing me what happened in other parts of the world during that time?