The only thing I can think of is to create a table called tbl9MoStart with a field called StartDate. Put in the starting date you want 1/4/2002 (dd/mm/yyyy) in the StartDate field (just the one record in this table). You can then reference that value in an expression in your query to give you the 9 month period. That expression would look like this:
INT(DateDiff("m",DLookUp("StartDate","tbl9MoStart" ),[Data e fillimit te tremujorit])/9)+1 AS 9MoPeriod
You would then group on this field in your report.