I solved it myself. Well, by no means alone, I used answers from this forum
and especially the source www.contextures.com.
I now know that if there are blanks in the list then grouping of dates into
months won't happen, and how to set up a named range that grows automatically
using the OFFSET function as shown in
www.contextures.com/xlPivot01.html#Dynamic.

My thanks to all

"Jonathan589" wrote:

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!)