Can time of possession for the two teams of an NFL game add up to less than 60 minutes?

Question

In a December 13, 2015 game between the Atlanta Falcons and Carolina Panthers, the time of possession of the two teams was recorded as:

Falcons: 28:21
Panthers: 31:21

Adding these two gives a total game time of 59:42, which is 18 seconds short of a full game. Is there an explanation for this? Or is this simply an error in the source data?

EDIT

Another game I found that has a similar discrepancy:

http://www.nfl.com/gamecenter/2004101711/2004/REG6/broncos@raiders#tab=analyze&analyze=boxscore

That is from NFL.com. It's one second short of a full game. Another error in the data?

Answer 1

You haven't added the source of data which may help in clarifying but official NFL website shows the possession of these two teams for this match as:

Falcons: 28:30
Panthers: 31:30
Total: 60

Source

ESPN also shows the same stat.

Source

So, 59:42 might be an error.