Puede resolver esto con un CTE recursivo
DECLARE @tbl TABLE (Case_Reference NVARCHAR(MAX),Narrative NVARCHAR(MAX));
INSERT INTO @tbl VALUES
(N'C1',N'01/02/2000 Some text with blanks 02/03/2000 More text 03/04/2000 An even more')
,(N'C2',N'01/02/2000 Test for C2 02/03/2000 One more for C2 03/04/2000 An even more 04/05/2000 Blah')
,(N'C3',N'01/02/2000 Test for C3 02/03/2000 One more for C3 03/04/2000 An even more')
;
WITH recCTE AS
(
SELECT 1 AS Step,Case_Reference,Narrative,CAST(1 AS BIGINT) AS StartsAt,NewPos.EndsAt+10 AS EndsAt,LEN(Narrative) AS MaxLen
,SUBSTRING(Narrative,NewPos.EndsAt+10+1,999999) AS RestString
FROM @tbl AS tbl
CROSS APPLY(SELECT PATINDEX('%[0-3][0-9]/[0-1][0-9]/[1-2][0-9][0-9][0-9] %',SUBSTRING(Narrative,12,9999999))) AS NewPos(EndsAt)
UNION ALL
SELECT r.Step+1,r.Case_Reference,r.Narrative,r.EndsAt+1,CASE WHEN NewPos.EndsAt>0 THEN r.EndsAt+NewPos.EndsAt+10 ELSE r.MaxLen END,r.MaxLen
,SUBSTRING(r.RestString,NewPos.EndsAt+10+1,999999)
FROM recCTE AS r
CROSS APPLY(SELECT PATINDEX('%[0-3][0-9]/[0-1][0-9]/[1-2][0-9][0-9][0-9] %',SUBSTRING(r.RestString,12,99999999))) AS NewPos(EndsAt)
WHERE r.EndsAt<r.MaxLen
)
SELECT Step,Case_Reference,StartsAt,EndsAt
,SUBSTRING(Narrative,StartsAt,EndsAt-StartsAt+1) AS OutputString
FROM recCTE
ORDER BY Case_Reference,Step
El resultado
+------+----------------+----------+--------+---------------------------------------+
| Step | Case_Reference | StartsAt | EndsAt | OutputString |
+------+----------------+----------+--------+---------------------------------------+
| 1 | C1 | 1 | 38 | 01/02/2000 Some text with blanks |
+------+----------------+----------+--------+---------------------------------------+
| 2 | C1 | 39 | 60 | 02/03/2000 More text |
+------+----------------+----------+--------+---------------------------------------+
| 3 | C1 | 61 | 84 | 03/04/2000 An even more |
+------+----------------+----------+--------+---------------------------------------+
| 1 | C2 | 1 | 24 | 01/02/2000 Test for C2 |
+------+----------------+----------+--------+---------------------------------------+
| 2 | C2 | 25 | 52 | 02/03/2000 One more for C2 |
+------+----------------+----------+--------+---------------------------------------+
| 3 | C2 | 53 | 77 | 03/04/2000 An even more |
+------+----------------+----------+--------+---------------------------------------+
| 4 | C2 | 78 | 93 | 04/05/2000 Blah |
+------+----------------+----------+--------+---------------------------------------+
| 1 | C3 | 1 | 24 | 01/02/2000 Test for C3 |
+------+----------------+----------+--------+---------------------------------------+
| 2 | C3 | 25 | 52 | 02/03/2000 One more for C3 |
+------+----------------+----------+--------+---------------------------------------+
| 3 | C3 | 53 | 76 | 03/04/2000 An even more |
+------+----------------+----------+--------+---------------------------------------+
