Thanks for sharing your code but it just doesn't need to be so complex a thing. SQL Server will handle all sorts of date formats without any help. The only time it really runs into a problem is where you have DMY and MDY formats in the same column so it wouldn't be able to figure out if 3/7/2005 is in March or July in a mixed column... just like your code won't be able to.
For code that follows one standard (eithe DMY or MDY) in a given column. No special processing for format is needed. For example:
SET DATEFORMAT DMY
SELECT SomeStringDate
, ConvertedToDateTime = CAST(d.SomeStringDate AS DATETIME)
FROM (
SELECT '15-03-05' UNION ALL
SELECT '15/03/08' UNION ALL
SELECT '15/03/2005' UNION ALL
SELECT '15.03.2005' UNION ALL
SELECT 'March 15 2005' UNION ALL
SELECT 'Mar 15 2005' UNION ALL
SELECT '15 March 2005' UNION ALL
SELECT '15 Mar 2005' UNION ALL
SELECT '20050315'
) d (SomeStringDate)
;
--Jeff Moden
Change is inevitable... Change for the better is not.