The following should do the work
This assumes the date is in the form dd/mm/yyyy: the seperators could be different as they are ignored anyway based on the substring.
The important thing to realise here is that the <xsl:sort> functions do not do anything APART from sort, so there is nothing to see at this point if debugging
The work is done in a receiving
The ensures items are delivered to this block in the correct order, what is displayed is determined in the section