I want another cell to evaluate if there is a date (of any kind) in another
cell. If there is then I want the formula to place the date minus 30 days.
If there's not, then I want it to say "NA".

Ex:
Cell A4 can have, "OK", "Overdue", or physically input a date. Cell A5 will
be A4-30, if there is a date. If there is not then A5 will read "NA".

Thanks