Optimizing key lookup in subquery with UNION ALL
Have you tried this?

SELECT Id, StatusDate, [ some way to select columns from appropiate table depending on result.tbl ]
FROM (
        SELECT Id, StatusDate, 'Results_201505' as tbl
        FROM Results_201505
        WHERE A = 0, B = 1, C = 3
    UNION ALL 
        SELECT Id, StatusDate, 'Results_201504' as tbl
        FROM Results_201504
        WHERE A = 0, B = 1, C = 3
    UNION ALL 
        SELECT Id, StatusDate, 'Results_201503' as tbl
        FROM Results_201503
        WHERE A = 0, B = 1, C = 3
    ORDER BY StatusDate DESC
    OFFSET xxx ROWS
    FETCH NEXT 25 ROWS ONLY
) AS result ;