The New York Times notes that it's taken three weeks, but this week TV networks finally found out how many people were really watching during the week their shows began new seasons. The bottom line: more viewers for most shows, especially the hits and those that appeal to younger viewers. Nielsen Media Research released figures for delayed viewing, and for most the numbers rose, with some adding three million or four million viewers. The premiere of "Grey's Anatomy" added more than 4.2 million viewers in playback, while "House," on Fox, added more than 3.7 million. But in the age group networks most care about, viewers ages 18 to 49, the percentage of improvement was striking for some shows, such as "Heroes" on NBC, which slid in its premiere ratings this year as compared with its live performance last year. Many of those viewers return when DVR playback was included.