How to copy across table headers that are dates?

I'm creating a table and I would like the headers to be month-end dates going across. However, once converted to a table and the headers copied across, it no longer recognizes the values as dates and instead copies across nonsensical dates.

The table will be an ongoing spreadsheet where the next month will be copied across and hopefully populates - I've never had this problem before.

Are you not allowed to have dates/formulas in table headers? None of these work

=TODAY()
=EOMONTH("",+1)
=DATE(YEAR(A1),MONTH(A1)+1,DAY(A1))

Thank you - but what about just simply selecting and copying across the dates as month-ends? Does the table not recognize that pattern?

Thought about that, but would prefer to just add a new column/month as needed.

I suppose I could just do that for 16,000 columns and be done with