It's a widely accepted piece of TV ratings dogma that same-day numbers represent a starting point, not the complete picture for a given show.

What's also true, however, is that in 2018-19, the starting point for nearly every returning broadcast series retreated from the previous season. 

In fact, only 10 percent (10 of 102) of veteran series increased or held steady with their same-day adults 18-49 rating from the 2017-18 season. The Hollywood Reporter's comparison includes same-day ratings for all original episodes of series that aired more than one episode in the 2018-19 season, including those coded as specials.

Only episodes that aired within the boundaries of the Nielsen-measured season (Sept. 24, 2018-May 22, 2019) are counted, which leaves out a handful of early-September football games and the odd early premiere.