Two indirect formulas with different results

[Berna11]

Good morning
I need your help to understand why the formulas you find in the TOTALE sheet file B-C column give 2 different results.
That of column B is correct but, I would like to use a formula that if I add more sheets in column E, it does not have to change every time the final reference of the last cell filled in E.
With the formula in column C it seemed to have solved but, as shown in line 5 in yellow, from 2 different results and I do not understand why.
Can you tell me, rectify or other formula that can give the correct result.
Thank you.