Grand Total values for Bookcases, chairs, furnishing & tables should display Quantity values as of Dec for selected Year & Month. As per enclosed *.twbx file, max month is Dec.
So my grand total should be 22,96,151 & 74
I do not know if we can change the Grandtotal to show the latest month.
But I tried showing the latest month using calculated fields. But they will need to be discrete values and will be shown before your monthly measures.
See if this will work for you.