For the accounts to which no NPS Survey is sent, the surveys (which are sent for other accounts) are still shown in the C360 section for that account. This information seems to be irrelevant for that Account.
To be more precise with my explanation, let us suppose there are two Accounts A & B. I have sent out NPS survey for Account A and not for Account B but still those survey show up in Account B's C360 with a score of zero.
Also, since we show and calculate the NPS Score of the last 6 NPS Surveys it is possible that even if there is a NPS Survey for Account B (sent before Account A's Survey), it will be overridden by Account A survey with zero score.
To help clarify, I think this is what Ankur is referring to:
In configuration for the NPS Section of the C360, you can specify that you'd like to see a calculated NPS score and the timeperiod over which this score should be calculated. See below where I select 365 days:
However, the issue can arise as the NPS Score widget only looks at the 7 most recent NPS surveys, so if there are more than 7 surveys that were sent in the last 365 days, then only the 7 most recent surveys will be calculated when determining the NPS score.