As you can see in the chart below, Blatt took the scripts for every episode (minus the six clip shows) and broke them down according to the number of scenes, which characters had the most lines, and how, in the case of the “Core Four” — Jerry, George, Elaine, and Kramer — how those lines stacked up against those allotted to the others. He found two major trends: One, the median number of scenes per episode steadily from every season until the second-to-last, ranging from a median of 10 for the first, abbreviated season of what was then called “The Seinfeld Chronicles” to 26 in season 8. Two, the percentage of lines spoken by the “Core Four” steadily converged, with Seinfeld dropping from 50 percent of the total in season 1 to around 35 percent in seasons 7 and 9, and George, Elaine and Kramer hovering around 20 percent each. The percentage of total lines spoken by secondary characters also rose, from 14 percent in season 1 to 30 percent in season 5, fluctuating after that between 27 and 30 until the series’ end. (Click through to Slate’s nifty interactive graphic to see precisely how the Core Four’s share of the total varied by episode and by season.)
In most ways, this seems like a typical sitcom evolution: My guess would be you’d get similar results for most long-running half hour shows. “Seinfeld” started out as a show about Jerry, with George — the onscreen representation of “Seinfeld’s” co-creator, Larry David — as a strong second. As the years progressed, and Jason Alexander, Julia Louis-Dreyfus and Michael Richards proved themselves invaluable members of the ensemble, they became almost as important to the show (and nearly as well-paid) as Seinfeld himself. Giving George, Elaine, and Kramer their own storylines necessarily meant boosting the role of secondary characters, many of whom became closely identified with the series. (You can probably guess who made the most frequent appearances of any non-Core Four figure: Wayne Knight’s Newman.)
As for the increase in scenes, that seems pretty organic as well. More characters, more storylines, plus the financial resources that come with one of the 1990s most successful network sitcoms: Voilà. You want another set? Go ahead and build one. That doesn’t of course, account for the slight dropoff in the final season, but that’s why numbers can only tell you so much.