table heading value not working

I have a table populated by a query and am adding a column at the end that becomes part of the table.
The problem I have is that I am trying to make the heading to the new column the value from another cell, which is a date, but it just shows the column heading as 00-jan-00. I have tried many different formats and various functions include just =$a$1, +$a$1, TEXT($a$1,dd-mmm-yy). I have even tried just getting part of the date from $a$1 such as YEAR($a$1).

The value in $a$1 is 18-NOV-15 and this does change, hence the fact I want the heading to reflect that value.

If I don't include the column as a table it works, but I need the column to be part of the table so that I can do a powerquery and include this column.

Hi

The Excel tables does not allow formulas as column headings, only constant values

Regards