I have a problem with a formula. Here is a very simplified version:

I have a worksheet set up with monthly sales of product A and B.
I use this worksheet to enter in the sales for A and B as well as returns
and a total is calculated.
At that point a copy is saved of this worksheet in the same workbook named
January.
Then the process start over for February and so on each month.
I have a Summary worksheet set up so sum these totals. Initially all the
formulas have #Ref! since the January, February through December worksheets
do not yet exist.
My problem is that once the January worksheet is created, the formula still
shows #Ref!. It doesn't recognize the January worksheet and pick up the
number for each of the products.

I tried to manually calculate, and update links. That didn't help

Any suggestions?