For duplicate rows, creating a column that shows status based on date

I am hoping for some help with the scenario below in SQL

Current State:

For a particular combination of med_id, casemgr_id, casemgr_clnt_id, the status should be reflected accordingly:

Desired Output:

In the first scenario, for med_id=98410, casemgr_id=12345, casemgr_clnt_id=67891, the date (1strow) is valid, but for the same rows, if the dates fall within 6 months, then the status should be invalid. In the second scenario, for med_id=91956, casemgr_id=99012, casemgr_clnt_id=87567, the date (1strow) is valid, but for the second row, the status is valid since the date is greater than 6 months. In summary, for duplicate rows for med_id, casemgr_id and casemgr_clntid, the status for the first row will be valid, but for the subsequent row, it will be valid id the date is > 6 months, otherwise it will be invalid if less than 6 months.

How do I achieve this in SQL? Please assist!

You can't without window functions, as @Jan Suchanek already showed.

Mine is similar - it also uses LAG(), but it uses some sort of "anchor" using FIRST_VALUE() , to use MONTHS_BETWEEN() upon:

WITH
-- your input ...
indata(id1,med_id,date,casemgr_id,casemgr_cln,status) AS (
          SELECT 123456,98410,DATE '4/19/24',12345,67891,-2
UNION ALL SELECT 789101,98410,DATE '4/24/24',122345,67891,-2
UNION ALL SELECT 234561,98410,DATE '4/25/24',12345,67891,-2
UNION ALL SELECT 567890,98410,DATE '4/26/24',12345,67891,-2
UNION ALL SELECT 456789,91956,DATE '4/20/24',99012,87567,-2
UNION ALL SELECT 998415,91956,DATE '12/20/24',99012,87567,-2
)
-- end of input, real query starts here ...
SELECT
  id1
, med_id
, date
, casemgr_id
, casemgr_cln
, CASE
    WHEN MONTHS_BETWEEN(
           date
         , FIRST_VALUE(date) OVER(PARTITION BY med_id, casemgr_id, casemgr_cln ORDER BY date)
         )  > 6
      OR MONTHS_BETWEEN(
           date
         , FIRST_VALUE(date) OVER(PARTITION BY med_id, casemgr_id, casemgr_cln ORDER BY date)
         )  = 0
    THEN 'valid'
    ELSE 'invalid'
  END AS status
FROM indata
ORDER BY med_id, casemgr_id, casemgr_cln, date 
;