@Pleu
I initially thought it meant what you describes but those numbers also do not add up.
I currently have 2 loops. On the mouse over It says I'm 7 days short of leveling up, but on NeededFoundDays I have 10 days with a value of 2.
The cacher I had seen with a loop of 53 (not 57 is I wrote earlier) have days with 46, 50, 51 and 52 finds on he's NeedFoundDays.