However, the fix is really simple. Since all we need in an anchor date of a monday, write this case statement.

--===== Test the new formula ============================================================

DECLARE @Bitbucket INT;

SELECT @Bitbucket = CASE

WHEN Date < '19000101' THEN DATEPART(dy,DATEDIFF(dd,'17530101',Date)/7*7+3)+6

ELSE DATEPART(dy,DATEDIFF(dd,'19000101',Date)/7*7+3)+6

end / 7

FROM #TestTable;

GO 5