sum columns only where all values (in rows) are available

[#1]

Hi, I have a table that summarizes the number of documents per different entities.

I am trying to create a graph which sums all document numbers - but only for rows which contain data through all selected months.

In the attached example, when I have all months selected I would like to get the sum only for entities DEDS + DEJP.

If left with Jul - Dec, I would get bars for CHEE + DEDS + DEJP + SEBH.

I hope I've made it clear.

I would appreciate help as I don't have a clue how to achieve this, if achievable. Maybe I need to add some information on LOAD?