Pivot update issue, renamed data column headers removes column from "Values" on update

Hi,

I have an issue updating my pivot.

The data area contains formulas resulting in week related output. Ex W2105, one week in every column. Next week the series are updated with new week numbers, one removed and one added.

upon refresh the the column with a new value is no longer in the list of Value.

The reference is the same, just the top row used as heading has changed. This is a snip of the table updated after 4 weeks. The 4 new week numbers are not selected.

Any way to get around this?