Try this... It's a liitle cumbersome and would benefit greatly from some proper indexes but it does apear to produce the desired results.

WITH
    cte_RowsToKeep AS (
        SELECT
            c.clientid,
            c.assessment_nbr,
            c.begin_dt,
            c.end_dt,
            c.date_died,
            KeepNum = MAX(c.assessment_nbr)...

Odds are you're just making it more difficult that it needs to be. First thing about SSRS is that there is no "report header" like there is with CR...
Before...

It's using the datatype of Col1, same as it is for f1, f2 & f3.

Please check out the following link...

Forum Etiquette: How to post data/code...

Here's a slightly different way of producing the same results...

WITH cteDays(Schedule_Days) AS (
SELECT N FROM (VALUES (0),(1),(2),(3),(4),(5),(6)) AS X(N)
)
SELECT
    t.ID,

Try this...

SELECT DISTINCT
    td1.Id
FROM
    #temp_data td1
WHERE
    NOT EXISTS (
            SELECT 1
            FROM
                #temp_data td2
            WHERE
                td1.Id = td2.Id

Here is a different solution that can build the string with a single pass at the table... (making it @ 1/3 the cost of the 3 pass solution).
[code...

Here's another set of options...

IF OBJECT_ID('tempdb..#Links','U') IS NOT NULL
    DROP TABLE #Links;

CREATE TABLE #Links (
        ClientRef INT,
        LinkedClientRef INT
    );
-- Create the data