Add a new column to your table e.g. RollingWeek smallint
update yourTable set RollingWeek=FinWeek where FinYear=2010
update yourTable set RollingWeek=FinWeek + 52 where FinYear=2011
update yourTable set RollingWeek=FinWeek + 105 where FinYear=2012
etc etc etc
then query for the difference between two dates :
e.g.
--= find weeks between 19th november 2010 and today 5th Jan 2011
select b.RollingWeek - a.RollingWeek as WeekDiff
from yourTable a, yourTable b
where a.theDate = '2010-11-19' AND b.theDate = '2011-01-05'
MM
select geometry::STGeomFromWKB(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