The 2012–13 television season officially passed into the Nielsen history books last night, bringing to an end what will likely be remembered as one of the worst years ever in the history of network TV (assuming, of course, that anyone still remembers what “television” is in 50 years). There were hardly any new breakout hits (though The Following, Revolution, and Elementary did okay). And, as has been widely reported, the Big Four as a whole bled viewers: They collectively lost about 10 percent of their adults-under-50 audience this season, with none of the major broadcasters growing year to year in the key demo. But as bad as things look on the macro level, the devastation is even more evident — and jaw-dropping — when you dig into the numbers for all the returning shows.

The vast majority of the nearly 90 series that had their second or higher season on ABC, CBS, NBC, Fox, and the CW lost ground among adults under 50. In the expandable chart below showing the year-to-year ratings change of all returning network shows, you’ll see that more than 50 series declined by double digits, nearly 30 fell by 20 percent or more, roughly a dozen gave back a quarter or more of their young audience, and an unlucky seven saw their ratings collapse by at least one-third. And in case you’re wondering, you can’t blame most of these losses on DVRs: The season’s Nielsen numbers include viewers who time-shift shows within a week of their initial broadcast. Overall, the chart paints a pretty ugly picture of where network TV stands right now. The good news for broadcasters: They get to wipe the slate clean and start all over again in just four months.

NOTES: Our chart is based on Nielsen data comparing all available viewing data for the season to date (through Sunday) against Nielsen’s final measurement for the 2011–12 season. Because Nielsen still needs to tally DVR data for the last couple of weeks of this season, the numbers we used for this season are not 100 percent complete. For most shows, this won’t change whether they’re up or down versus last season. However, in the case of shows that had a very small drop this year, like Grey’s Anatomy, The Middle, NCIS, NCIS: Los Angeles, Suburgatory, and Revenge, it’s possible that the final numbers will show the series either flat or up a tick, rather than their current status as “down” compared to last season. And Person of Interest, currently shown as flat, may yet rise to “up” when all numbers are tallied.