You can do this as following.
SELECT distinct '99991', tbl_DisclosureTypeDetails.disclodetDisclosureId,isnull( tbl_Disclosures.Disclosures,'') AS Expr1, (SELECT TOP 1 DATE_COLUMN FROM SOMEOTHERTABLE WHERE [CONDITION]) AS NEWCOLUMN
FROM .......
The other way is to store the column in a temp table and update the date column afterwards and finally return the result form the temp table.