Using an IF argument & COUNTIF argument in the same cell formula

Hi guys,

I have a datasheet with a list of test references along with the dates they were tested. Many test references appear multiple times as they have come forward again for re-testing, therefore I have used a COUNTIF formula to determine where this is the case and provide all of the dates it has been tested for ease of reference.

The problem I am having is that I would only like to show dates prior to a certain test date , rather than just a list of all dates it has matched a reference to.

I have attached a spreadsheet as an example: TESTA.xlsx

So, if looking at the Test Date in cell A13 which is 11-10 - this reference was previously tested on 18-04, 06-06, 25-08 and 11-10 however preferably only 18-04, 06-06 and 25-08 would be showing. Likewise, with cell A5 18-04 is duplicated again which is also something I would like to remove.

Any advice would be much appreciated!

Thanks all,

Tom