You can do this with the DATEDIF() function. This is what I got:
01-Feb-09 04-Feb-10 LONG
09-Feb-09 04-Feb-10 SHORT
using this formula:
=IF(DATEDIF(A26,B26,"y")>0,"LONG","SHORT")where A26 contained purchase/start date and B26 contained sold/end date.
DATEDIF() with "y" returns the completed number of years between dates. If less than a full year it returns zero.
The IF function returns the Long/Short text based on the value from DATEDIF()
PS Not sure about more recent versions of Excel, but this function does not appear in help files for Excel 2003, but it still works.