Brian is correct that you really shouldn't need to be entering hard-coded dates into formulas.
To achieve what you need.
1. Create a new sheet (called "CompanyDates") containing the dates that are deemed to be 'company holidays'
2 Enter this formula:
This will check the date in cell B2 and return a '--' if the date is not in the company holiday list or 1 if it is.
Even if more dates are added to the list (next year) it will still work.