I have 12 monthly workbooks with one section that summarises the data for the
month into about 10 sections. So, in the summary I have about 10 rows, with
basic formula
B100=sum(B2:B10)
B101=sum(B11:B20) and so on.

I have another workbook for the year that references the cells in the summary

My question is, if I have both the workbooks open(current month and year),
and I insert a new row, the summary will change to B101=sum(B2:B10) and the
reference in the yearly workbook will be updated as well.
If the yearly workbook is closed, and I insert a new row into the current
month, the refernce will not update in the yearly workbook, it will still try
to reference B100

Do both workbooks have to be open?