Hi,

I've partially solved item 2 of the OP by using a combination of converting the date number to three strings containing the dd/md/yyyy, recombining these into a string but swapping the day & month over, and finally converting the modofied string back to a date number. The formula below does not directly relate to the Original workbook since I had added some intermediate columns whilst testing it.

=VALUE(TEXT(IF(ISNUMBER(J3),DATE(TEXT(YEAR($J3),0),TEXT(DAY($J3),0),TEXT(MONTH($J3),0)),J3),0))
However I'm still looking for a solution to Q1 if anyone can suggest anything.