Pivot tables off a List

I’ve a big XL2003 table to which records are added every day or two, and a
couple of pivot tables analyse out what I want nicely, except …

I want counts and sums by month, where the column fields are the dates from
the records list. I want to group the dates into months. Following advice
from this forum I discovered that the table would not group my dates into
months if there were blanks, so it works if I just select populated rows.

But I have the source data set up as a List so that others can enter new
records. If I select the list including the new-entry row I get a blank. How
do I get this to let me group dates into months to show a constantly-evolving
table, yet allow new records to be added to the source data?

(I hope I'm not missing something simple and obvious!)