A Google News Help thread has a complaint that the number shown in the "sources" section of Google News clusters is wrong.
Here is an example, this says 3 but it leads to 4 sources:
I honestly never thought the number was exact. I though it was an estimate, like the number of search results shown in Google. But a Google representative replied like it is a bug.
Google's Archi Sarkar-Goyal said:
Thanks Lmobi for reporting this. We are working on resolving on this issue soon.
Makes you wonder...
Forum discussion at Google News Help.