A careful restudy of the sunspot numbers reported by dozens of solar observatories around the globe and averaged in the Solar Influences Data Analysis Center at the Royal Observatory of Belgium has found some discrepancies, often based on individual observers’ idiosyncrasies. (See Section 10.2, p. 265 and Figure 10-18a, p. 268.)
The Center has provided the following revised sunspot count for this revision of The Cosmos, 4th ed. It is updated, too, past the recent solar maximum, which peaked at different times in different solar hemispheres.