update: now confirmed. And this explanation via an AP story is...something (emphasis mine):
Nielsen explained the discrepancy of more than 3 million viewers by saying a more complete check of their records revealed additional viewership on some digital tier networks. The company hadn't been aware that they were showing the game.
we hear from a reliable source or two that after additional counting Sunday night's Super Bowl featuring an awesome contest where the Pittsburgh Steelers ultimately defeated the Arizona Cardinals is now the most-watched Super Bowl ever, eclipsing even last year's game which averaged 97.448 million, with a 98.7 million average.
Previously it had been reported that Sunday night's game averaged 95.4 million, which would've made it the second most-watched Super Bowl of all time.
We still haven't seen the data, but if true, we will see it in any number of ways including an "Super Bowl XLIII Second Most Watched Super Bowl Ever" press release from NBC.
Here is the updated press release via NBC (nice headline!):
MOST VIEWED TV PROGRAM IN HISTORY: SUPER BOWL XLIII ON NBC
151.6 Million Total Viewers
& 98.7 Million Average Viewers Watch Super Bowl XLIII
TAMPA – Feb. 3, 2009 – Super Bowl XLIII is now the most viewed television program in U.S. history with a total audience of 151.6 million viewers, according to official national ratings data released today by Nielsen Media Research.
"It's always incredibly satisfying to amass large audiences, but this television record simply reaffirms the power of the Super Bowl and the National Football League," said Dick Ebersol, Chairman, NBC Universal Sports & Olympics. "Everyone associated with the NFL should feel a great sense of pride in this accomplishment and in providing a day of enjoyment to American families – especially those who are struggling in these difficult times."
MOST VIEWED TELEVISION PROGRAMS IN HISTORY (total viewers):
1. Super Bowl XLIII 151.6 million NBC 2009
2. Super Bowl XLII 148.3 million Fox 2008
3. Super Bowl XXVIII 144.4 million CBS 2004
The total audience of 151.6 million viewers tops the previous Super Bowl record audience of 148.3 million viewers by 3.3 million viewers (Super Bowl XLII, Giants-Patriots, Note: total audience measures viewership for all or part of a broadcast).
MOST-WATCHED SUPER BOWLS (average viewers):
1. Super Bowl XLIII 98.7 million NBC 2009
2. Super Bowl XLII 97.5 million Fox 2008
3. Super Bowl XXX 94.1 million NBC 1996
4. Super Bowl XLI 93.2 million CBS 2007
5. Super Bowl XXVII 91.0 million NBC 1993
The average viewership of 98.7 million is tops in Super Bowl history, beating last year's game by 1.2 million viewers (97.5 million). NBC now owns two of the top three and three of the top five most watched Super Bowls of all-time, with Super Bowl XXX third on the list with 94.1 million viewers and Super Bowl XXVII fifth with 91.0 million viewers. (Note: P2+ measures average viewership per minute). * The M*A*S*H finale in 1983 averaged 106 million viewers and total audience figures for the program are estimated to be 122 million viewers.