Hi Nigel,
In Numbers, see if this idea suits your needs.
13 Sheets in one document.
The first Sheet (named Year) contains a single-cell table where you type the year.

The second Sheet is named January. It contains one table with a Header Row and 31 Body Rows.

In cell A1, type the name of the month formatted as Text.
Formula in A2 (and Fill Down) =DATE(Year::$A$1,MONTH(A$1),ROW()−1)
For the screen shot, I hid some rows.
Duplicate the January Sheet 11 times.
Change the names to February, March etc.
Type the name of the month in A1 of each Sheet (as Text).
For each 30 day month, delete the last row (it will show the 1st of the next month and is not needed).
February is a special case. You need 29 Body Rows to allow for Leap Years. In non Leap Years, it will show 1st March. If you can just ignore that, all is good.

Change the year on the "Year" Sheet to 2020 and February correctly shows 29 February.

There are no links between months; they are independent. The only link between Sheets is to the "Year" Sheet to look up the year.
Regards,
Ian.