Letter from Sherrie

I started recently reading your mother’s Pern series in publishing order, then decided to read them in chronological order, starting with the landing. Was there a book written for the years/turn of the first interlude of thread fall in the time from year 28 through year 100 when the first weyrleader was chosen and how the first harper was chosen?

I can’t find any reference for this time. The next ref. is 275 years later.