In the Tools -> Delete tab
While in the Post itself
Perhaps only one digit displayed in the first??
The default filter on the delete list is 2 days:
So the post has 20 delete votes total, but only 2 in the last two days. It actually only has 2 in the last 30 days, so widening the filter that far won't help, but the counts of other posts can change (for example, For statement in C has 18 delete votes, all in the last month but only 1 recently, so it says "1" on the 2d/7d/14d views, but 18 on the 30d -- 17 were between 15 and 30 days ago)